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Dark Matter Substructure in the Simulations and Observed Universe. P. Nurmi. Pure N-body vs. Hydro. Collisionless N-body (DM only) simulations ( accurate solution to an idealized problem) - Ω m is WIMP and is distributed as N particles - PowerPoint PPT Presentation
Citation preview
2212008 Tuorla Observatory
1
Dark Matter Substructure in the Simulations and Observed Universe
P Nurmi
2212008 Tuorla Observatory
2
Pure N-body vs Hydro
Collisionless N-body (DM only) simulations (accurate solution to an idealized problem)- Ωm is WIMP and is distributed as N particles- problems in the center of galaxies where baryons dominate- only gravity- high resolution- no free parameters (ICs taken from CMB)Hydrodynamical simulations (approximate solution to a more realistic problem)- computationally expensive relatively low resolution- complicated (SPH and grid codes often disagrees)- important physical processes typically act on scales far below resolution and are implemented through uncertain functions and free parameters
2212008 Tuorla Observatory
3
Cosmological N-body Simulations
Our simulations 6 different simulations with 3 different resolutions and 2 different simulation codes (AMIGA and GADGET-2)
Louhi Cray XT4
2212008 Tuorla Observatory
4
Subhalo-galaxy connection
For large halos Mtotasymp 1013 - 1015
MSunhMain halo= massive ldquoellipticalrdquo galaxy
Substructure = normal galaxies
For small halos Mtotasymp 1011 - 1013
MSunhMain halo = typical spiral galaxy
Substructure = dwarf galaxy
5-10 of total mass are in substructures dNdm~m-18plusmn01
2212008 Tuorla Observatory
5
Substructure in the DM (only) simulations
Two sets of slides
1 Z-evolution of all halos in the 40 Mpch simulation An interesting region is shown with several merger events
2 Zoom of substructure in the 20 Mpch simulation of a system with 241013 MSunh and containing 275 subhalos Subhalo masses are between 109 MSunh and 1011 MSunh
2212008 Tuorla Observatory
7
2212008 Tuorla Observatory
8
2212008 Tuorla Observatory
9
Mass accretion history of subhalosZentner amp Bullock ApJ 598 2005(semi-analytic)
Most accretedsubhalos are destroyed
Some general results confirmed by many studies
1 Most of the mass is accreted in large ~1011Msun subhalos
2 Majority of accreted systems are destroyed before z=0
3 Surviving substructure is generally young
2212008 Tuorla Observatory
10
2212008 Tuorla Observatory
11
2212008 Tuorla Observatory
12
Dynamical and physical evolution of subhalos
Tidal effects- mainhalo-subhalo encounters subhalo-subhalo encountersDepends on the halo profile and halo masses- Leads to massloss profile changes etc
Dynamical frictionDynamical friction arises because of the wake of particles that grow behind the motion of particle due to gravitational focusing- Orbital changes
2212008 Tuorla Observatory
13
Some problems concerning substructure
bull Overmerging a problem related to resolution
(White (1976) van Kampen (1995))
bull Abundance of CDM structure match galaxy abundance in clusters but not in local group satellites
(Moore at al (1999))
bull Spatial distribution of subhalos they are too far from the center
(Diemand (2004))
bull Some improvement by selecting subhalos according to
mass (or circular velocity) before accretion
(Nagai amp Kravtsov (2005) Conroy at al (2006))
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
2
Pure N-body vs Hydro
Collisionless N-body (DM only) simulations (accurate solution to an idealized problem)- Ωm is WIMP and is distributed as N particles- problems in the center of galaxies where baryons dominate- only gravity- high resolution- no free parameters (ICs taken from CMB)Hydrodynamical simulations (approximate solution to a more realistic problem)- computationally expensive relatively low resolution- complicated (SPH and grid codes often disagrees)- important physical processes typically act on scales far below resolution and are implemented through uncertain functions and free parameters
2212008 Tuorla Observatory
3
Cosmological N-body Simulations
Our simulations 6 different simulations with 3 different resolutions and 2 different simulation codes (AMIGA and GADGET-2)
Louhi Cray XT4
2212008 Tuorla Observatory
4
Subhalo-galaxy connection
For large halos Mtotasymp 1013 - 1015
MSunhMain halo= massive ldquoellipticalrdquo galaxy
Substructure = normal galaxies
For small halos Mtotasymp 1011 - 1013
MSunhMain halo = typical spiral galaxy
Substructure = dwarf galaxy
5-10 of total mass are in substructures dNdm~m-18plusmn01
2212008 Tuorla Observatory
5
Substructure in the DM (only) simulations
Two sets of slides
1 Z-evolution of all halos in the 40 Mpch simulation An interesting region is shown with several merger events
2 Zoom of substructure in the 20 Mpch simulation of a system with 241013 MSunh and containing 275 subhalos Subhalo masses are between 109 MSunh and 1011 MSunh
2212008 Tuorla Observatory
7
2212008 Tuorla Observatory
8
2212008 Tuorla Observatory
9
Mass accretion history of subhalosZentner amp Bullock ApJ 598 2005(semi-analytic)
Most accretedsubhalos are destroyed
Some general results confirmed by many studies
1 Most of the mass is accreted in large ~1011Msun subhalos
2 Majority of accreted systems are destroyed before z=0
3 Surviving substructure is generally young
2212008 Tuorla Observatory
10
2212008 Tuorla Observatory
11
2212008 Tuorla Observatory
12
Dynamical and physical evolution of subhalos
Tidal effects- mainhalo-subhalo encounters subhalo-subhalo encountersDepends on the halo profile and halo masses- Leads to massloss profile changes etc
Dynamical frictionDynamical friction arises because of the wake of particles that grow behind the motion of particle due to gravitational focusing- Orbital changes
2212008 Tuorla Observatory
13
Some problems concerning substructure
bull Overmerging a problem related to resolution
(White (1976) van Kampen (1995))
bull Abundance of CDM structure match galaxy abundance in clusters but not in local group satellites
(Moore at al (1999))
bull Spatial distribution of subhalos they are too far from the center
(Diemand (2004))
bull Some improvement by selecting subhalos according to
mass (or circular velocity) before accretion
(Nagai amp Kravtsov (2005) Conroy at al (2006))
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
3
Cosmological N-body Simulations
Our simulations 6 different simulations with 3 different resolutions and 2 different simulation codes (AMIGA and GADGET-2)
Louhi Cray XT4
2212008 Tuorla Observatory
4
Subhalo-galaxy connection
For large halos Mtotasymp 1013 - 1015
MSunhMain halo= massive ldquoellipticalrdquo galaxy
Substructure = normal galaxies
For small halos Mtotasymp 1011 - 1013
MSunhMain halo = typical spiral galaxy
Substructure = dwarf galaxy
5-10 of total mass are in substructures dNdm~m-18plusmn01
2212008 Tuorla Observatory
5
Substructure in the DM (only) simulations
Two sets of slides
1 Z-evolution of all halos in the 40 Mpch simulation An interesting region is shown with several merger events
2 Zoom of substructure in the 20 Mpch simulation of a system with 241013 MSunh and containing 275 subhalos Subhalo masses are between 109 MSunh and 1011 MSunh
2212008 Tuorla Observatory
7
2212008 Tuorla Observatory
8
2212008 Tuorla Observatory
9
Mass accretion history of subhalosZentner amp Bullock ApJ 598 2005(semi-analytic)
Most accretedsubhalos are destroyed
Some general results confirmed by many studies
1 Most of the mass is accreted in large ~1011Msun subhalos
2 Majority of accreted systems are destroyed before z=0
3 Surviving substructure is generally young
2212008 Tuorla Observatory
10
2212008 Tuorla Observatory
11
2212008 Tuorla Observatory
12
Dynamical and physical evolution of subhalos
Tidal effects- mainhalo-subhalo encounters subhalo-subhalo encountersDepends on the halo profile and halo masses- Leads to massloss profile changes etc
Dynamical frictionDynamical friction arises because of the wake of particles that grow behind the motion of particle due to gravitational focusing- Orbital changes
2212008 Tuorla Observatory
13
Some problems concerning substructure
bull Overmerging a problem related to resolution
(White (1976) van Kampen (1995))
bull Abundance of CDM structure match galaxy abundance in clusters but not in local group satellites
(Moore at al (1999))
bull Spatial distribution of subhalos they are too far from the center
(Diemand (2004))
bull Some improvement by selecting subhalos according to
mass (or circular velocity) before accretion
(Nagai amp Kravtsov (2005) Conroy at al (2006))
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
4
Subhalo-galaxy connection
For large halos Mtotasymp 1013 - 1015
MSunhMain halo= massive ldquoellipticalrdquo galaxy
Substructure = normal galaxies
For small halos Mtotasymp 1011 - 1013
MSunhMain halo = typical spiral galaxy
Substructure = dwarf galaxy
5-10 of total mass are in substructures dNdm~m-18plusmn01
2212008 Tuorla Observatory
5
Substructure in the DM (only) simulations
Two sets of slides
1 Z-evolution of all halos in the 40 Mpch simulation An interesting region is shown with several merger events
2 Zoom of substructure in the 20 Mpch simulation of a system with 241013 MSunh and containing 275 subhalos Subhalo masses are between 109 MSunh and 1011 MSunh
2212008 Tuorla Observatory
7
2212008 Tuorla Observatory
8
2212008 Tuorla Observatory
9
Mass accretion history of subhalosZentner amp Bullock ApJ 598 2005(semi-analytic)
Most accretedsubhalos are destroyed
Some general results confirmed by many studies
1 Most of the mass is accreted in large ~1011Msun subhalos
2 Majority of accreted systems are destroyed before z=0
3 Surviving substructure is generally young
2212008 Tuorla Observatory
10
2212008 Tuorla Observatory
11
2212008 Tuorla Observatory
12
Dynamical and physical evolution of subhalos
Tidal effects- mainhalo-subhalo encounters subhalo-subhalo encountersDepends on the halo profile and halo masses- Leads to massloss profile changes etc
Dynamical frictionDynamical friction arises because of the wake of particles that grow behind the motion of particle due to gravitational focusing- Orbital changes
2212008 Tuorla Observatory
13
Some problems concerning substructure
bull Overmerging a problem related to resolution
(White (1976) van Kampen (1995))
bull Abundance of CDM structure match galaxy abundance in clusters but not in local group satellites
(Moore at al (1999))
bull Spatial distribution of subhalos they are too far from the center
(Diemand (2004))
bull Some improvement by selecting subhalos according to
mass (or circular velocity) before accretion
(Nagai amp Kravtsov (2005) Conroy at al (2006))
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
5
Substructure in the DM (only) simulations
Two sets of slides
1 Z-evolution of all halos in the 40 Mpch simulation An interesting region is shown with several merger events
2 Zoom of substructure in the 20 Mpch simulation of a system with 241013 MSunh and containing 275 subhalos Subhalo masses are between 109 MSunh and 1011 MSunh
2212008 Tuorla Observatory
7
2212008 Tuorla Observatory
8
2212008 Tuorla Observatory
9
Mass accretion history of subhalosZentner amp Bullock ApJ 598 2005(semi-analytic)
Most accretedsubhalos are destroyed
Some general results confirmed by many studies
1 Most of the mass is accreted in large ~1011Msun subhalos
2 Majority of accreted systems are destroyed before z=0
3 Surviving substructure is generally young
2212008 Tuorla Observatory
10
2212008 Tuorla Observatory
11
2212008 Tuorla Observatory
12
Dynamical and physical evolution of subhalos
Tidal effects- mainhalo-subhalo encounters subhalo-subhalo encountersDepends on the halo profile and halo masses- Leads to massloss profile changes etc
Dynamical frictionDynamical friction arises because of the wake of particles that grow behind the motion of particle due to gravitational focusing- Orbital changes
2212008 Tuorla Observatory
13
Some problems concerning substructure
bull Overmerging a problem related to resolution
(White (1976) van Kampen (1995))
bull Abundance of CDM structure match galaxy abundance in clusters but not in local group satellites
(Moore at al (1999))
bull Spatial distribution of subhalos they are too far from the center
(Diemand (2004))
bull Some improvement by selecting subhalos according to
mass (or circular velocity) before accretion
(Nagai amp Kravtsov (2005) Conroy at al (2006))
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
7
2212008 Tuorla Observatory
8
2212008 Tuorla Observatory
9
Mass accretion history of subhalosZentner amp Bullock ApJ 598 2005(semi-analytic)
Most accretedsubhalos are destroyed
Some general results confirmed by many studies
1 Most of the mass is accreted in large ~1011Msun subhalos
2 Majority of accreted systems are destroyed before z=0
3 Surviving substructure is generally young
2212008 Tuorla Observatory
10
2212008 Tuorla Observatory
11
2212008 Tuorla Observatory
12
Dynamical and physical evolution of subhalos
Tidal effects- mainhalo-subhalo encounters subhalo-subhalo encountersDepends on the halo profile and halo masses- Leads to massloss profile changes etc
Dynamical frictionDynamical friction arises because of the wake of particles that grow behind the motion of particle due to gravitational focusing- Orbital changes
2212008 Tuorla Observatory
13
Some problems concerning substructure
bull Overmerging a problem related to resolution
(White (1976) van Kampen (1995))
bull Abundance of CDM structure match galaxy abundance in clusters but not in local group satellites
(Moore at al (1999))
bull Spatial distribution of subhalos they are too far from the center
(Diemand (2004))
bull Some improvement by selecting subhalos according to
mass (or circular velocity) before accretion
(Nagai amp Kravtsov (2005) Conroy at al (2006))
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
8
2212008 Tuorla Observatory
9
Mass accretion history of subhalosZentner amp Bullock ApJ 598 2005(semi-analytic)
Most accretedsubhalos are destroyed
Some general results confirmed by many studies
1 Most of the mass is accreted in large ~1011Msun subhalos
2 Majority of accreted systems are destroyed before z=0
3 Surviving substructure is generally young
2212008 Tuorla Observatory
10
2212008 Tuorla Observatory
11
2212008 Tuorla Observatory
12
Dynamical and physical evolution of subhalos
Tidal effects- mainhalo-subhalo encounters subhalo-subhalo encountersDepends on the halo profile and halo masses- Leads to massloss profile changes etc
Dynamical frictionDynamical friction arises because of the wake of particles that grow behind the motion of particle due to gravitational focusing- Orbital changes
2212008 Tuorla Observatory
13
Some problems concerning substructure
bull Overmerging a problem related to resolution
(White (1976) van Kampen (1995))
bull Abundance of CDM structure match galaxy abundance in clusters but not in local group satellites
(Moore at al (1999))
bull Spatial distribution of subhalos they are too far from the center
(Diemand (2004))
bull Some improvement by selecting subhalos according to
mass (or circular velocity) before accretion
(Nagai amp Kravtsov (2005) Conroy at al (2006))
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
9
Mass accretion history of subhalosZentner amp Bullock ApJ 598 2005(semi-analytic)
Most accretedsubhalos are destroyed
Some general results confirmed by many studies
1 Most of the mass is accreted in large ~1011Msun subhalos
2 Majority of accreted systems are destroyed before z=0
3 Surviving substructure is generally young
2212008 Tuorla Observatory
10
2212008 Tuorla Observatory
11
2212008 Tuorla Observatory
12
Dynamical and physical evolution of subhalos
Tidal effects- mainhalo-subhalo encounters subhalo-subhalo encountersDepends on the halo profile and halo masses- Leads to massloss profile changes etc
Dynamical frictionDynamical friction arises because of the wake of particles that grow behind the motion of particle due to gravitational focusing- Orbital changes
2212008 Tuorla Observatory
13
Some problems concerning substructure
bull Overmerging a problem related to resolution
(White (1976) van Kampen (1995))
bull Abundance of CDM structure match galaxy abundance in clusters but not in local group satellites
(Moore at al (1999))
bull Spatial distribution of subhalos they are too far from the center
(Diemand (2004))
bull Some improvement by selecting subhalos according to
mass (or circular velocity) before accretion
(Nagai amp Kravtsov (2005) Conroy at al (2006))
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
10
2212008 Tuorla Observatory
11
2212008 Tuorla Observatory
12
Dynamical and physical evolution of subhalos
Tidal effects- mainhalo-subhalo encounters subhalo-subhalo encountersDepends on the halo profile and halo masses- Leads to massloss profile changes etc
Dynamical frictionDynamical friction arises because of the wake of particles that grow behind the motion of particle due to gravitational focusing- Orbital changes
2212008 Tuorla Observatory
13
Some problems concerning substructure
bull Overmerging a problem related to resolution
(White (1976) van Kampen (1995))
bull Abundance of CDM structure match galaxy abundance in clusters but not in local group satellites
(Moore at al (1999))
bull Spatial distribution of subhalos they are too far from the center
(Diemand (2004))
bull Some improvement by selecting subhalos according to
mass (or circular velocity) before accretion
(Nagai amp Kravtsov (2005) Conroy at al (2006))
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
11
2212008 Tuorla Observatory
12
Dynamical and physical evolution of subhalos
Tidal effects- mainhalo-subhalo encounters subhalo-subhalo encountersDepends on the halo profile and halo masses- Leads to massloss profile changes etc
Dynamical frictionDynamical friction arises because of the wake of particles that grow behind the motion of particle due to gravitational focusing- Orbital changes
2212008 Tuorla Observatory
13
Some problems concerning substructure
bull Overmerging a problem related to resolution
(White (1976) van Kampen (1995))
bull Abundance of CDM structure match galaxy abundance in clusters but not in local group satellites
(Moore at al (1999))
bull Spatial distribution of subhalos they are too far from the center
(Diemand (2004))
bull Some improvement by selecting subhalos according to
mass (or circular velocity) before accretion
(Nagai amp Kravtsov (2005) Conroy at al (2006))
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
12
Dynamical and physical evolution of subhalos
Tidal effects- mainhalo-subhalo encounters subhalo-subhalo encountersDepends on the halo profile and halo masses- Leads to massloss profile changes etc
Dynamical frictionDynamical friction arises because of the wake of particles that grow behind the motion of particle due to gravitational focusing- Orbital changes
2212008 Tuorla Observatory
13
Some problems concerning substructure
bull Overmerging a problem related to resolution
(White (1976) van Kampen (1995))
bull Abundance of CDM structure match galaxy abundance in clusters but not in local group satellites
(Moore at al (1999))
bull Spatial distribution of subhalos they are too far from the center
(Diemand (2004))
bull Some improvement by selecting subhalos according to
mass (or circular velocity) before accretion
(Nagai amp Kravtsov (2005) Conroy at al (2006))
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
13
Some problems concerning substructure
bull Overmerging a problem related to resolution
(White (1976) van Kampen (1995))
bull Abundance of CDM structure match galaxy abundance in clusters but not in local group satellites
(Moore at al (1999))
bull Spatial distribution of subhalos they are too far from the center
(Diemand (2004))
bull Some improvement by selecting subhalos according to
mass (or circular velocity) before accretion
(Nagai amp Kravtsov (2005) Conroy at al (2006))
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
14
Large-scale galaxy clustering
Two-point correlation functions calculated from the halos in ΛCDM-simulations and galaxies from SDSS agree very well (Conroy et al 2006 ApJ 647)-gt dots = SDSS solid line = ART simulations 512sup3 in (80 Mpch)sup3
Similar results from Virgo Consortium simulations in larger scales (Springel et al 2005 Nature 435)-gt 2160sup3 in (500 Mpch)sup3
Also the galaxy formation physics incorporated in the SPH simulation give a good account of observed galaxy clustering (Weinberg et al 2005 ApJ 601) [144sup3 in (50 Mpch)sup3 cube]
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
15
Comparison between SDSS galaxy data and our simulations
Abell 2151 The Hercules Galaxy Cluster
SDSS DR5 data ΛCDM simulations
Typical halo with several subhalos (galaxies)
Rvir
The 25-meter SDSS survey telescope
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
16
How to populate halos with galaxies(a major problem to DM-simulations)
We can use a simplified procedure (varying ML function) that is based on the analytical fit that gives luminosity when halo mass is given (Vale amp Ostriker 2004 MNRAS 353)
We test if this is statistically satisfied by using another method in which suitable galaxies that resemble DM halos and subhalos are selected from the Millenium run semi-analytic galaxy catalogue
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
17
SDSS DR5 galaxy group sample
Observational ingredient is based on the galaxy group catalogue by Tago et al (2007)
From this data we select three volume limited samples based on the group distance dlt100 Mpch dlt200 Mpch and dlt300 Mpch and SDSS completeness limit mr(lim)=175 This gives us three luminosity limits for galaxies that are included in the analysis
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
18
Comparison 1 Richness
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
19
Comparison 2a Luminosity (all galaxies that have L gt Llim(d) are included for observations Lgroup is
corrected for invisible galaxies)
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
20
But what about small subhalos around Milky Way sized halos
A simple DM halo mass ndash Luminosity correlation does not work anymore
Too many subhalos if compared with observed dwarf galaxies
ldquoClassicalrdquo Dwarf Galaxy Problem
(Moore et al 1999)
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
21
Scientific context small-scale galaxy clustering -gt missing dwarf problem
Basically all cosmological simulations predict that there are at least one order of magnitude more small subhalos (dwarf galaxies) around Milky Way like galaxies than what is observed (eg Via Lactea simulation Diemand et al 2007 ApJ 657)-gt234 million particles in (90 Mpch)sup3 multimass simulation mp=20900 Msun
Recently discovered (from SDSS data) ultra-faint dwarfs with ML~1000 help to solve this discrepancy but not fully (factor of 4 difference) However If reionization occurred around redshift 9 minus 14 and dwarf galaxy formation was strongly suppressed thereafter the circular velocity function of Milky Way satellite galaxies approximately matches that of CDM subhalos in Via Lactea simulation (Simon and Geha 2007 astro-ph 07060516)
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
22
Can MW dwarfs be used at all for comparison
(Kroupa et al 2005AampA 431 517)
ldquoThe shape of the observed distribution of Milky Way (MW) satellites is inconsistent with their being drawn from a cosmological sub-structure population with a confidence of 995 per cent Most of the MW satellites therefore cannot be relate to dark-matter dominated satellitesrdquo
If the MW dwarfs do indeed constitute the shining fraction of DM sub-structures then their number-density distribution should be consistent with an isotropic (ie spherical) or oblate power-law radial parent distribution
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
23
But also in simulations accretions are an-isotropic and large subhalos tend to be more accreted along the major axis of the host halo
Consistent if the major axis of MW halo is perpendicular to Galactic disk (Kang Mao Jing Gao 2005)
Great Disk (pancake) has thickness ~ 20kpc~ perpedicular to the MW disk
Can MW dwarfs be used at all for comparison
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
24
Other Groups(Karachentsev AJ 129 178 2005)
- Good targets (M31 M81 M83)
- There is maybe some signal but it is much weaker
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
25
Radial distribution of subhalos
(Willman et al MNRAS 353 (2004) 639-646 )
Incompleteness needs to be taken seriously
Radial distribution of the oldest subhalos in a Lambda+CDM simulation of a Milky Way-like galaxy possess a close match to the observed distribution of M31s satellites which suggests that reionization may be an important factor controlling the observability of subhalos
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
26
Observational signature of substructure
2 Gravitational Lensing - Galaxy substructure may explain the flux ratio anomalies observed in multiply-imaged lensed QSOs- Milliarcsecond scale image splitting of quasars that are known to be splitted on arcsecond level (Zackrisson et al 2008)One major problem is the density profile of small subhalos
1 Satellite Galaxies of MW Most massive DM subhalos are associated with luminous dSph satellites Problem most dark matter subhalos appear to have no optically luminous counterparts in the Local Group (ldquomissing satellite problemrdquo)
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
27
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
28
Is it possible to observe substructure by strong gravitational lensing
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
29
Observational signature of substructure
3 Dark Matter AnnihilationBecause of their high phase-space densities subhalos may be detectablevia γ-rays from DM particle annihilation in their cores (Diemand Kuhlen amp Madau 2006) (GLAST VERITAS)
4 Tidal streams Presence of a population of CDM clumps alters the phase-space structure of a globular cluster tidal stream If the global Galactic potential is nearly spherical this corresponds to a broadening of the stream from a thin great-circle stream into a wide band on the sky (Ibata et al 2002) (GC streams detectable by GAIA)
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
30
Observational signature of substructure
5 Signatures of long-term dynamical effects of subhalos to galaxiesSatellite-disk encounters of the kind expected in CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way M31 and in other nearby and distant disk galaxies (Kazantsidis et al 2007)
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
31
Conclusions
Cdm models predict several close encounters of massive subhalos with the galactic disks since zlt1 Unless a mechanism (gas accretion) can somehow stabilize the disks to these violent gravitational encounters stellar disks as old and thin as the Milky Wayrsquos will have severe difficulties to survive typical satellite accretion within ΛCDM
Kazantzidis 2007 arXiv07081949v1
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
2212008 Tuorla Observatory
32
Summary
The galaxy-halo-subhalo-DM connection is not yet fully understood
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