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Dark MatterASTR 333/433
Fall 2013MoTu 4:00-5:15pm
Sears 552
Prof. Stacy McGaughSears 573368-1808
Logistics:
• Abstracts for 433 talks due now• 433 talks 12/2 & 12/3 (next week)• Homework 4 due 12/3• Review 12/9 (11 AM)• Final 12/11 (9 AM)
Today: MOND
What gets us into trouble is not what we don’t know.
It’s what we know for sure that just aint so.
- Mark Twain
A few things we know for sure...
∇2Φ = 4πGρF = ma
which basically means
mV2/R = GMm/R2
i.e,
V2 = GM/R
The universe is filled with non-baryonic cold dark matter.
ergo...
Newton saysV2 = GM/R.Equivalently,Σ = M/R2
V4 = G2MΣ
ThereforeDifferent Σshould meandifferent TF
normalization.
μ = -2.5 logΣ +C
TF Relation
No residuals from TF with size or surface density for disks
V 2 =GM
R⇥ � log(V )
� log(R)= �1
2 expected slope (dotted line)
large range in size at a given mass or velocity
Note:
For disk galaxies
Newton says: V 2
R=
GM
R2= G(�b + �DM )
� =M
R2surface density
So we infer that �DM � �b
(i.e., that all disks are dark matter dominated)in order to explain the lack of TF residuals with luminous size Rp
But we also infer that the baryons do matter...
3. Gravitational force correlates with baryonic surface density
central baryonic surface density
acceleration at peak of baryonic rotation curvea � �1/2
b
(would be linear if just Newton with no dark matter)
Lack of TF residuals says baryon distribution does not matter.
V 2
R= G (�b + �DM )
Correlation of dynamical force with observed surface density says the baryon distribution does matter.
But wait - before we decided �b � �DM
Now is observed to correlate with gravitational force. Is this a contradiction?
⌃b
or maybe w
e’ve been using the wrong equation
74 galaxies> 1000 points
(all data)
60 galaxies> 600 points(errors < 5%)
radius
orbitalfrequency
acceleration
McGaugh (2004)
Not just any force law...
No unique size scale in the data. Can generically exclude any modification of gravity where a change in the force law appears at a specific length scale.
There is a characteristic acceleration scale in the data
a = gN for a ≫ a0
µ
(
a
a0
)
a = gN
µ(x) → 1 for x ≫ 1 µ(x) → x for x ≪ 1
a =√
gNa0 for a ≪ a0
MONDModified Newtonian Dynamics (Milgrom 1983)
a0
Instead of invoking dark matter, modify gravity (or inertia). Milgrom suggested a
modification at a particular acceleration scale
x =
a
a0
∇
[
µ
(
∇Φ
a0
)
∇Φ
]
= 4πGρ
Derived from aquadratic Lagrangian of Bekenstein & Milgrom (1984) to satisfy energy conservation.
(t,x) ! �(t,x)MOND regime invariant under transformations
Newtonian regime MOND regime
Regimes smoothly joined by
Modified Poisson equation
• The Tully-Fisher Relation
• Slope = 4
• Normalization = 1/(a0G)
• Fundamentally a relation between Disk Mass and Vflat
• No Dependence on Surface Brightness
• Dependence of conventional M/L on radius and surface brightness
• Rotation Curve Shapes
• Surface Density ~ Surface Brightness
• Detailed Rotation Curve Fits
• Stellar Population Mass-to-Light Ratios
MOND predictions
“Disk Galaxies with low surface brightness provide particularly strong tests”
None of the following data existed in 1983.At that time, LSB galaxies were widely
thought not to exist.
• The Tully-Fisher Relation
• Slope = 4
• Normalization = 1/(a0G)
• Fundamentally a relation between Disk Mass and Vflat
• No Dependence on Surface Brightness
• Dependence of conventional M/L on radius and surface brightness
• Rotation Curve Shapes
• Surface Density ~ Surface Brightness
• Detailed Rotation Curve Fits
• Stellar Population Mass-to-Light Ratios
MOND predictions
✔✔✔
✔ !
In MOND limit of low acceleration
a =
√
gNa0
V 2
R=
√
GM
R2a0
V4
= a0GM
observed TF!
• The Tully-Fisher Relation
• Slope = 4
• Normalization = 1/(a0G)
• Fundamentally a relation between Disk Mass and Vflat
• No Dependence on Surface Brightness
• Dependence of conventional M/L on radius and surface brightness
• Rotation Curve Shapes
• Surface Density ~ Surface Brightness
• Detailed Rotation Curve Fits
• Stellar Population Mass-to-Light Ratios
MOND predictions
✔✔✔
✔
✔
• The Tully-Fisher Relation
• Slope = 4
• Normalization = 1/(a0G)
• Fundamentally a relation between Disk Mass and Vflat
• No Dependence on Surface Brightness
• Dependence of conventional M/L on radius and surface brightness
• Rotation Curve Shapes
• Surface Density ~ Surface Brightness
• Detailed Rotation Curve Fits
• Stellar Population Mass-to-Light Ratios
MOND predictions
✔✔✔
✔
✔
✔
• The Tully-Fisher Relation
• Slope = 4
• Normalization = 1/(a0G)
• Fundamentally a relation between Disk Mass and Vflat
• No Dependence on Surface Brightness
• Dependence of conventional M/L on radius and surface brightness
• Rotation Curve Shapes
• Surface Density ~ Surface Brightness
• Detailed Rotation Curve Fits
• Stellar Population Mass-to-Light Ratios
MOND predictions
✔✔✔
✔
✔
✔
✔
surface brightness
mas
s su
rfac
e de
nsity
= V
2 /(G
h)
Not
a fit
MO
ND
D
In NGC 6946, a tiny bulge (just 4% of thetotal light) leaves a distinctive mark.
NGC 6946
D
In NGC 1560, a marked feature in the gas is reflected in the kinematics, even though dark matter should be totally dominant.
NGC 1560
Sand
ers &
McG
augh
200
2, A
RA&
A, 40,
263
Sand
ers &
McG
augh
200
2, A
RA&
A, 40,
263
Sand
ers &
McG
augh
200
2, A
RA&
A, 40,
263
Residuals of MOND fits
Famaey, B., & McGaugh, S.S. 2012, Living Reviews in Relativity, 15, 10
• The Tully-Fisher Relation
• Slope = 4
• Normalization = 1/(a0G)
• Fundamentally a relation between Disk Mass and Vflat
• No Dependence on Surface Brightness
• Dependence of conventional M/L on radius and surface brightness
• Rotation Curve Shapes
• Surface Density ~ Surface Brightness
• Detailed Rotation Curve Fits
• Stellar Population Mass-to-Light Ratios
MOND predictions
✔✔✔
✔
✔
✔
✔
✔
Line: stellar population model(mean expectation)
• The Tully-Fisher Relation
• Slope = 4
• Normalization = 1/(a0G)
• Fundamentally a relation between Disk Mass and Vflat
• No Dependence on Surface Brightness
• Dependence of conventional M/L on radius and surface brightness
• Rotation Curve Shapes
• Surface Density ~ Surface Brightness
• Detailed Rotation Curve Fits
• Stellar Population Mass-to-Light Ratios
MOND predictions
✔✔✔
✔
✔
✔
✔
✔
✔
Example utility: our own Galaxy
You are here
8 kp
c
Example utility: our own Galaxy
Put in mass distribution (Flynn et al 2006);Get out rotation curve (no fitting)
Luna et al. (2006: CO); McClure-Griffiths & Dickey (2007: HI); Xue et al. (2008: BHB)
You
are
here
McGaugh, S.S. 2008, ApJ, 683, 137
stel
lar d
isk
edge
Recovering surface density from rotation velocity:
Σ(R) =V 2
2πGR
Σ(R) =1
2πG
[
1
R
∫ R
0
dV 2c
drK
(
r
R
)
dr +
∫
∞
R
dV 2c
drK
(
R
r
)
dr
r
]
only works for spheres.
For disks, need
which has a proclivity to blow up.
Instead, do by trial and error
Can we do better?
McGaugh, S.S. 2008, ApJ, 683, 137
Can we do better fitting the details of the terminal velocity curve?
Luna et al. (2006: CO); McClure-Griffiths & Dickey (2007: HI); Xue et al. (2008: BHB)
Fitting the details of the terminal velocity curve
Fitting the details of the terminal velocity curve
Fitting the details of the terminal velocity curve
Fitting the details of the terminal velocity curve
Fitting the details of the terminal velocity curve
Milky Way structure
Surface density
total
gas
disk
bulge
Bovy & Rix (2013)
Bovy & Rix (2013)
Surface density from radial and vertical force in good agreement
I find your lack of faith disturbing.
• You don’t know the Power of the Dark Side
• Can MOND explain large scale structure?
• Can it provide a satisfactory cosmology?
• Can it be reconciled with General Relativity?
Review of relativistic theoriescontaining MOND in the appropriate limit
• You don’t know the Power of the Dark Side
• Can MOND explain large scale structure?
• Can it provide a satisfactory cosmology?
• Can it be reconciled with General Relativity?
7.1 Scalar-tensor k-essence 7.2 Stratified theory 7.3 Original Tensor-Vector-Scalar theory 7.4 Generalized Tensor-Vector-Scalar theory 7.5 Bi-Scalar-Tensor-Vector theory 7.6 Non-minimal scalar-tensor formalism 7.7 Generalized Einstein-Aether theories 7.8 Bimetric theories 7.9 Dipolar dark matter 7.10 Non-local theories and other ideas
{Famaey, B., & McGaugh, S.S. 2012, Living Reviews in Relativity, 15, 10
Bruneton - maximum acceleration inevitable in quantum gravity
I find your lack of faith disturbing.
• You don’t know the Power of the Dark Side
• Can MOND explain large scale structure?
• Can it provide a satisfactory cosmology?
• Can it be reconciled with General Relativity?
• Does it survive other tests?
Clusters problematic
Clusters of galaxies
(Sanders & McGaugh 2002)
dark matter shouldn’t needdark matter
1E 0657-56 - “bullet” cluster (Clowe et al. 2006)
direct proof of dark matter?
bullet cluster shows samebaryon discrepancy in MOND
as other galaxy clusters
MOND𝚲CDM
Famaey, B., & McGaugh, S.S. 2012, Living Reviews in Relativity, 15, 10
discrepancy in clusters appears real. LCDM not much better
observed shock velocity
CDM
bullet cluster collision velocity
Angus & McGaugh (2008) MNRAS, 383, 417
observed shock velocity
MOND
bullet cluster collision velocity
Angus & McGaugh (2008) MNRAS, 383, 417
Bullet cluster
• Mass discrepancy more naturally explained with dark matter.
• Collision velocity more naturally explained with MOND.
Bournaud et al. (2007) Science, 316, 1166
Tidal Debris Dwarfs - should be devoid of Dark Matter
Gentile et al. (2007)A&A, 472, L25
Tidal dwarfsdo show mass
discrepancies asexpected in MOND
A new test: the dwarf satellites of Andromeda
McGaugh & Milgrom 2013, ApJ, 766, 22; also ApJ, 775, 139
gin < gex < a0gin < a0 < gex
gin < a0gin > a0
Newtonian regime MOND regime
External Field dominantquasi-Newtonian regime
External Field dominantNewtonian regime
M =
RV 2
G
M =
RV 2
G
M =
a0
gex
RV 2
G
M =
V 4
a0G
e.g.,Eotvos-type
experiment on the surface of
the Earth
e.g.,remotedwarfLeo I
e.g.,nearbySgr
dwarf
e.g.,surfaceof theEarth
And XVII 2.60E+05 381 2.9 2.5
And XXVIII 2.10E+05 284 4.9 4.3
Name Luminosity Re �obs
�pred
isolated
EFE
• In some flavors of relativistic theories, e.g., TeVeS, what matters is the potential gradient.
‣ Predicts strong effects at saddle points between massive bodies (e.g., sun-planet)
• MOND violates the Strong Equivalence Principle, leading to the External Field Effect - the Galactic field might matter in the Solar System.
‣ Predicts modest precession of outer planets
There can be more subtle effects
Galianni et al. arXiv:1111.6681
EarthMoon
to Sun
⇥�� 0
near saddle point,so
|gN|a0
becomes small,and strong MONDeffects can occurin a small region (theory specific,e.g., TeVeS - Bekenstein & Magueijo 2006)
SP
contours of phantom dark matter
• Disk Stability • Freeman limit in surface brightness distribution• thin disks• velocity dispersions • LSB disks not over-stabilized
• Dwarf Spheroidals
• Giant Ellipticals
• Clusters of Galaxies
• Structure Formation
• Microwave background• 1st:2nd peak amplitude; BBN• early reionization• enhanced ISW effect• 3rd peak
Other MOND tests
✔✔✔
✔
✔
✔
?
✔✔
✔
X
XNo MetricDon’t know expansion history
XX