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The Complex Web of Galaxy The Complex Web of Galaxy FormationFormation
Richard BowerRichard BowerAndreea Font, Ian McCarthy, Andrew BensonAndreea Font, Ian McCarthy, Andrew Benson
& the GALFORM team& the GALFORM teamUsing semi-analytic models to create a holistic approach to galaxy ecology.
Nature vs NutureNature vs Nuture
1.1. Are the differences due to evolutionary Are the differences due to evolutionary processes? (nurture)processes? (nurture)
2.2. Or due to intrinsic differences in progenitor’s Or due to intrinsic differences in progenitor’s mass? (nature)mass? (nature)
All most everyone focuses on (1)All most everyone focuses on (1) The universe is hierarchicalThe universe is hierarchical Clusters are formed out of smaller systemsClusters are formed out of smaller systems
3. A new twist - central vs satellite galaxies3. A new twist - central vs satellite galaxies
z = 0.0
The taxonomy of ecological models
The “classical” view
•Galaxies contain lots of cold gas
•They must fight to retain their cold gas
The “modern” view
•Galaxies rapidly deplete their cold gas
•They must continually be refueled
The post-modern view:
Properties only depend on mass and central/satellite
Springel et al 2005
Larson, Tinsley & Caldwell 1984
Gunn & Gott, 1972
Van den Bosch et al 2008
MechanismsMechanisms
Why should galaxy properties depend on the environment?
Ram-pressure Ram-pressure Collisions / harassmentCollisions / harassment "Strangulation""Strangulation"
Removal of cold disk gas
Removal of hot gas halo
Current thinking Current thinking (circa 2007):(circa 2007):
Ram-pressureRam-pressure: : only densest regions – most galaxies only densest regions – most galaxies
have lost their gas before this becomes have lost their gas before this becomes importantimportant
Collisions / harassmentCollisions / harassment: : important in shaping morphology, but important in shaping morphology, but
not so important in using up gasnot so important in using up gas““Strangulation”Strangulation”: :
the most important mechanism. In fact the most important mechanism. In fact its often too strong.its often too strong.
What the data say…What the data say…
Constraining models: The Constraining models: The Colour-Magnitude diagramColour-Magnitude diagram
CMR - a good tool for CMR - a good tool for studying clustersstudying clusters Simple, integrated coloursSimple, integrated colours ……but dust obscurred and but dust obscurred and
metal dependentmetal dependent
……or SFR directly?or SFR directly? Direct comparison of Direct comparison of
physical quantitiesphysical quantities Needs high quality Needs high quality
spectra and/or UV dataspectra and/or UV data
This is a theory talk, so I This is a theory talk, so I won’t make an issue of this.won’t make an issue of this.
Baldry et al. 2003 (see also Hogg et al. 2003)
Baldry et al. 2003
(u-r)
For a better analysis, take slices through the CMR:
Colour distribution in 0.5 mag bins can be fit with two Gaussians
Mean and dispersion of each distribution depends strongly on luminosity
Dispersion includes variation in dust, metallicity, SF history, and photometric errors
Bright
Faint
(u-r)
Fraction of star forming Fraction of star forming galaxies suppressed in galaxies suppressed in dense environments – dense environments – but it’s a continuous but it’s a continuous trendtrend
Local density is more Local density is more important than halo important than halo mass mass
Luminosity is more Luminosity is more important than important than environmentenvironment
isolated galaxiesisolated galaxies Even isolated regions Even isolated regions
contain “passive” galaxiescontain “passive” galaxiesBalogh et al. 2004
The colour-magnitude diagramThe colour-magnitude diagram
The post-modern view: satellite The post-modern view: satellite colours depend weakly on halocolours depend weakly on halo
Van den Bosch 2008
But clearly the “details” do depend on stellar mass.
Even at fixed mass, there are
•more red-sequence galaxies in higher mass haloes
• Radial gradients within systems (Smith et al 2008)
Can this be explained by tidal stripping, or reduced or more extended suppression ?
Mean and spread depend only weakly on stellar mass.
Stellar mass
halo mass
the post-modern viewthe post-modern view
Satellite vs central - importantSatellite vs central - importantEnvironment (aka halo mass) unimportantEnvironment (aka halo mass) unimportantNo special processesNo special processesTimescale for SF decay.Timescale for SF decay.
less important!
(updated)
( just one? stripping of halo gas?)
(needs to be quite long compared to halo lifetime)
Qualitative explanation Qualitative explanation of the trends of the trends
The strong dependence on galaxy massThe strong dependence on galaxy mass Nature? ie., the halo mass before accretionNature? ie., the halo mass before accretion
The subtle dependence on environment?The subtle dependence on environment? Immediately galaxies become satellites?Immediately galaxies become satellites? Or “Pre-processing” in groups?Or “Pre-processing” in groups?
But what fraction of galaxies fall directly into clusters? But what fraction of galaxies fall directly into clusters? ((Berrier et al 2008; McGee et al 2009)
A long timescale for suppression? A long timescale for suppression? …but not too long!
Let’s test the qualitative ideas with semi-analytic models
Semi-analytic modelsSemi-analytic models
And what AGN feedback can And what AGN feedback can do for you…do for you…
Croton et al 2006, Bower et al 2006
Some good things about Some good things about semi-analytic modelssemi-analytic models
Current models Current models seem to do seem to do reasonably well …. reasonably well …. (I’m sure someone will contradict (I’m sure someone will contradict me!)me!)
Present-day Present-day luminosity functionsluminosity functions
The transition massThe transition mass Galaxy down-sizingGalaxy down-sizing
The models achieve The models achieve this by suppressing this by suppressing cooling in high mass cooling in high mass haloeshaloes
See also Croton et al., De Lucia et al.; Kitzbichler et al., Somerville et al 2008
Semi-Analytic models:Semi-Analytic models:The state of the artThe state of the art
AGN + semi-analytic galaxy formation provides AGN + semi-analytic galaxy formation provides a frame work for understanding the “anti-a frame work for understanding the “anti-hierarchical” universehierarchical” universe
B06 is by no means the only model to use AGN: eg., Hatton et al 2003, B06 is by no means the only model to use AGN: eg., Hatton et al 2003, Granato et al ‘04, Croton et al. ‘06, De Lucia et al ‘07, Menci et al ‘07, Granato et al ‘04, Croton et al. ‘06, De Lucia et al ‘07, Menci et al ‘07, Cattaneo ‘07, Summerville ‘08 - but be aware of the different flavours.Cattaneo ‘07, Summerville ‘08 - but be aware of the different flavours.
The model seems to describe the properties of The model seems to describe the properties of central galaxies reasonably well…central galaxies reasonably well…
But..But.. …do they explain the environment-driven trends?
Problems with the Problems with the standard model…standard model…
Satellites are too red. Satellites are too red. Regardless of halo Regardless of halo mass.mass.
The effect of The effect of “strangulation” is “strangulation” is overestimatedoverestimated
A satellite galaxy A satellite galaxy orbiting within another orbiting within another halo is assumed to halo is assumed to loose its own hot gas loose its own hot gas reservoir.reservoir. This is far too simplisticThis is far too simplistic
Weinmann et al 2006; Baldry et al 2006.
Environmental Physics is not Environmental Physics is not correctly handledcorrectly handled
All satellites are red!
All GalaxiesSatellite Galaxies
No blue satellites!
Environmental Physics is not Environmental Physics is not correctly handledcorrectly handled
Is this realistic?
•Mass ratio of haloes
•Gas atmosphere of the main halo
Old Strangulation model
•Remove gas reservoir as galaxy orbits larger halo
Hot gas reservoir
SNe winds quickly exhaust disk gas
Larson, Tinsley & Caldwell 1984
Strangulation = suffocation = starvation
McCarthy et al 2007 – an improved model for halo stripping – depends on the orbit of the satellite and the gas content of the satellite and main halo.
(Actually, Gunn & Gott’s formulae re-calibrated for halo gas using numerical simulations)
Solving the problem by adjusting Solving the problem by adjusting the environment physicsthe environment physics
Dramatic improvement in the environmental dependence of satellite Dramatic improvement in the environmental dependence of satellite properties from reducing the effects of starvation.properties from reducing the effects of starvation.
Font et al 2008, also Kang & vdBosch 2008; Kimm et al 2009
A closer look at the colour A closer look at the colour distribution of galaxiesdistribution of galaxies
The Field The Clusters
Gilbank & Balogh 2008; Font, McGee, Balogh et al, in prep.
(Distributions shifted to to agree with red-sequence colours)
Too many intermediate colour galaxies, not enough blue objects
Too many faint red galaxies
Towards a holistic Towards a holistic modelmodel
Model improvements:Model improvements:
Including tidal strippingIncluding tidal stripping..needed to remove faint red galaxies..needed to remove faint red galaxies
Towards an accurate model of the intra-group Towards an accurate model of the intra-group mediummedium even the new stripping calculation is too even the new stripping calculation is too
aggressiveaggressive……needed to get ram pressure calculations rightneeded to get ram pressure calculations right
X-ray Emission from X-ray Emission from Groups and ClustersGroups and Clusters
L-T relation : well known L-T relation : well known that the self-similar that the self-similar relation failsrelation fails
AGN: standard model just AGN: standard model just prevents cooling… it prevents cooling… it doesn’t affect the X-ray doesn’t affect the X-ray luminosityluminosity
Data from Horner et al.
B06 Model
Data from Osmond & Ponman
The AGN feedback loop The AGN feedback loop (new version)(new version)
CoolingAGN
fuelling
Hydrostatic ?
Heating
redistribute halo gas Based on the “excess energy”
method (Wu et al 1999), plus the hydrostatic criterion
“radio” mode
P=min(Ledd,Mcool)
A note for pundits:
•This is “in-situ” heating
• there’s no “pre-heating”
•its going to be expensive, but not prohibitively so.
X-ray Emission from X-ray Emission from Groups and ClustersGroups and Clusters
L-T relation : well L-T relation : well known that the self-known that the self-similar relation failssimilar relation fails
AGN: standard model AGN: standard model just prevents coolingjust prevents cooling
Revised model, AGN Revised model, AGN feedback redistributes feedback redistributes halo gas until the halo gas until the cooling rate drops and cooling rate drops and AGN power is cut offAGN power is cut off
AGN redistributes halo gas
Scatter driven by diverse assembly history
Voit & Bryan 2001; Bower et al 2008, MN, in press (astro-ph/0808.2994)
A huge step forward - I’ve been trying to achieve this
for ten years!
Conclusions: what you should Conclusions: what you should remember!remember!
The classical view: The classical view: Galaxies contain lots of cold gas and fight to retain their cold gas
The modern view: The modern view: Galaxies rapidly deplete their cold gas and must continually be refueled
Post-modern view: Post-modern view: central or satellite - that’s all!
Lengthens the timescale of “starvation”
The properties of (faint) satellites are [somewhat] dependent on their parent halo
“nature” wins (the mass of the halo before accretion)
Conclusions: what you should Conclusions: what you should remember!remember!
Galaxy formation models:Galaxy formation models: ‘‘06 models: a reasonable 06 models: a reasonable
description of centralsdescription of centrals need to be modified to calculate need to be modified to calculate
environmental effects properlyenvironmental effects properly ‘‘08 models match some 08 models match some
satellite properties reasonably satellite properties reasonably wellwell……but the details still aren’t there but the details still aren’t there
yet…yet…
Post-modern view is rather too Post-modern view is rather too easily accommodated!easily accommodated!
Improvements and Improvements and challengeschallenges
Model Improvements:Model Improvements: Tidal stripping - Tidal stripping -
removing faint red removing faint red galaxies; reproducing galaxies; reproducing the intra-cluster lightthe intra-cluster light
Better modeling the Better modeling the intra-group medium, intra-group medium, understanding the X-understanding the X-ray haloes of groups ray haloes of groups and galaxiesand galaxies
Observational Observational challenges:challenges: Pushing low-redshift Pushing low-redshift
measurements to fainter measurements to fainter galaxies [GAMA, galaxies [GAMA, a wide-field a wide-field redshift survey 2mag deeper than redshift survey 2mag deeper than
SDSS (pi Norberg)SDSS (pi Norberg)]] Establishing robust Establishing robust
measurements for low measurements for low mass galaxies at higher mass galaxies at higher redshift. [ROLES, redshift. [ROLES, Gilbank et Gilbank et
al 2009;al 2009; zCOSMOS++?] zCOSMOS++?]
Redshift One Redshift One Emission Line SurveyEmission Line Survey
LDSS 3 on MagellanLDSS 3 on Magellan
Gilbank, Davies, Li, Balogh, Glazebrook, Hau, Bower, Gilbank, Davies, Li, Balogh, Glazebrook, Hau, Bower, Baldry, Savaglio, McCarthyBaldry, Savaglio, McCarthy
Thank you!Thank you!
How many parameters do How many parameters do semi-analytic models have?semi-analytic models have?
Post-modern view is rather Post-modern view is rather too easy!too easy!
Beyond the “modern” viewBeyond the “modern” view
Weinmann et al 2006; Van dev Bosch et al 2008
…but the differences between panels are largely due to the properties of central galaxies