Transcript Formation des Galaxies - Observatoire de Paris

Formation of
Galaxies
Dynamics of Galaxies
Françoise COMBES
Large-scale structures in Local Universe
Amas et superamas proches
2
Gott et al (03)
Conformal map
Logarithmic
Great Wall SDSS
1370 Mpc
80% longer than
CfA2 Great Wall
3
Large surveys of galaxies
CfA-2 18 000 galaxy spectra (1985-95)
SSRS2, APM..
SDSS: Sloan Digital Sky Survey: 1 million galaxy spectra
images of 100 millions objects, 100 000 Quasars
1/4 of sky surface (2.5m telescope)
Apache Point Observatory (APO), Sunspot, New Mexico, USA
2dF GRS: Galaxy Redshift Surveys: 250 000 galaxy spectra
AAT-4m, Australia et UK (400 spectra simultaneously)
4
5
2dF Galaxy Redshift Survey
250 000 galaxies, Colless et al (2003)
6
Comparaison between CfA2 & SDSS (Gott 2003)
7
Principles of Formation
A still unsolved problem
Several fondamental ideas:
gravitationnal instability,
Jeans critical size
In a Universe in expansion, structures do not collapse
exponentially, but develop in a linear manner
du/dt +(u grad)u = -grad F -1/r grad p;
d r /dt + div u =0
DF = 4p G r
Initial density fluctuations
dr /r << 1
definition dr /r = d
8
free-fall time tff = (G r 1) -1/2
Expansion time-scale texp = (G < r >) -1/2
Structures grow following the universe
characteristic radius d ~ R(t) ~ (1 + z)-1
For baryons, which can grow only
after recombination at z ~1000
The growth factor would be only of 103,
 insufficient, since fluctuations at this
epoch are only of 10-5
Last scattering surface/epoch (COBE, WMAP)
dT/T ~ 10-5 at large scale
9
Expansion of Universe & redshift
10
The sky is uniform at l=3mm
Once the constant level subtracted
 dipole ( V = 600km/s)
After subtraction of the dipole,
 The Milky Way, emission
of the dust, synchrotron, etc..
Subtraction of the Milky Way
 Random fluctuations
DT/T ~ 10-5
11
Universe homogeneous
& isotrope until the
recombination and the
collapse of structures
Last scattering surface
Epoch of t=380 000 yrs
Anisotropies measured
in the cosmological
background radiation
12
WMAP Results
Wm = 0.26
L = 0.74
Wb =0.04
Ho = 71km/s/Mpc
Age = 13.7 Gyr
Flat Universe
13
The parameters of the Universe
Anisotropies of the CMB
Observations of SN Ia
Gravitationnal lenses
14
A simple perturbation
Creates a depression
 Sound wave at c /√3
Sound Horizon
at recombination
R~150Mpc
Galaxies
in over-densities
 Acoustic waves
15
Multiple perturbations
16
Only the non-baryonic matter, which particles do not interact
with photons, or only through gravity,
Can start to grow before recombination,
Just after the epoch of equivalence matter-radiation
The dark matter can thus grow in density before the baryons, at all
scales after equality, but grow only perturbations of scale larger than
the horizon before equality (free streaming)
z > z eq
Radiation
l > ct d ~(1 + z) -2
l < ct d~ cste
z < zeq
Matter
d ~(1 + z) -1
d ~(1 + z) -1
17
r ~ R-3 matter
r ~ R-4 photons
Point of Equivalence E
Radiation
r
NEUTRAL
Matter
IONISED
104
z
103
Time 
18
Growth of adiabatic
fluctuations
At scales of 1014Mo
(8 Mpc)
They grow until they
contain the horizon mass
Then stay constant
(calibration t=0, arrow)
 The matter fluctuations (…) "standard model" follow
the radiation, and grow only after the Recombination R
 The CDM fluctuations grow from the point E
equivalence matter -radiation
19
Power spectrum
Theory of inflation: One suppose the spectrum scale independent,
And the power law such that the perturbations always enter the
horizon with the same amplitude
dr /r ~ dM/M = A M-a
a = 2/3, ou d(k)2 = P(k) = kn avec n=1
P(k) ~k at large scale
but P(k) tilted n= -3
At small scale (Peebles 82)
Comes from the streaming effect
For scales below the horizon
20
Fluctuations of density
Tegmark
et al21 2004
Fractales and Structure of the Universe
Galaxies are not distributed homogeneously on the sky
but along filaments, following a hierarchy
Galaxies gather in groups, then in galaxy clusters
themselves included in superclusters (Charlier 1908, 1922,
Shapley 1934, Abell 1958).
In 1970, de Vaucouleurs discovers an universal law
Density  size -a with a = 1.7
Benoît Mandelbrot in 1975: invents the name « fractal »
extension at the Universe
Regularity emerges from the random distributions
22
Galaxy catalogue CfA 2
23
Density of structures in the Universe
Solar System 10-12 g/cm3
Milky Way 10-24 g/cm3
Local Group 10-28 g/cm3
Galaxy clusters 10-29 g/cm3
Super-cluster 10-30 g/cm3
Density of photons (3K) 10-34 g/cm3
Critical density (W=1) 10-29 g/cm3
24
What is the upper limit scale of the fractal?
100 Mpc, 500 Mpc?
Correlations: inadequate formalism
(one cannot define an average density)
Density around an occupied point
G ( r )  r-g
On the figure, slope g = -1
Corresponding to D = 2
M ( r ) ~ r2
25
Hierarchical Formation
In the model the most adapted today to observations
CDM (cold dark matter), the first structures to grow are the
smallest, then larger ones grow by mergers (bottom-up)
| dk|2 =P(k) ~ kn, with n=1
At large scales
n= -3 at small scales
tilt when ρr ~ ρm
At the horizon scale
dM/M ~M-1/2 -n/6
when n > -3, hierarchical
formation (dM/M )
Abel & Haiman 00
26
Hierarchical galaxy
formation
The smallest structures form first,
with the typical sizes of
dwarf galaxies or globular clusters
By successive mergers and accretion
more and ore massive systems
form
They are less and less dense (expansion)
M  R2
& r  1/R
27
Numerical Simulations
With initial fluctuations
postulated gaussian, the
non-linear regime can be followed
Mainly for le gas and the baryons
(CDM easily taken into account
through semi-analytic models,
à la Press-Schechter)
28
29
Gas
Dark matter CDM
Simulations
(Kauffmann et al)
Galaxies
30
4 « phases »
4 Zoom levels
from 20 to 2.5 Mpc.
z = 3. (from. z=10.)
31
Multi-zoom Technique
Objective:
Evolution of a galaxy
(0.1 to 10 kpc)
Accretion of gas
(10 Mpc)
32
Semelin & Combes 2003
Galaxies and Filaments
Multi-zoom
33
Baryonic acoustic peaks
Wavess detected today
In the distribution of baryons
50 000 galaxies SDSS
Eisenstein et al 2005
34
Baryonic Oscillations: a standard ruler
Alcock & Paczynski (1979)
Test of cosmological constant
Observer
Can test the bias b
Galaxies/dark matter
cDz/H
DqD
Eisenstein et al. (2005)
50 000 galaxies SDSS
cDz/H = DqD
Possibility to
determine H(z)
35
Hypotheses for the CDM particles
Particles which are no longer relativistic at decoupling: COLD
Particles WIMPS (weakly interactive massive particles)
Neutralino: the lightest supersymmetric particle LSP
Relic of the Big-Bang, should disintegrate in gamma rays
(40 Gev- 5Tev)
May be lighter particles, or with more non-gravitationnal
interaction? (Boehm et al 04, 500kev INTEGRAL)
Actions (solution to the strong-CP problem, 10-4 ev)
Primordial black holes?
36
Direct and indirect searches
Could be produced in the new generation accelerators (LHC, 14TeV)
Direct search: CDMS-II, Edelweiss, DAMA, GENIUS, etc
Indirect search: gamma from annihilation (Egret, GLAST, Magic)
Neutrinos (SuperK, AMANDA, ICECUBE, Antares, etc)
Indirect
Direct
No detection up to now
37
Hypotheses for the dark baryons
Baryons in compact objects (brown dwarves, white dwarves,
black holes) are now ruled out by micro-lensing experiments
or suffer from major problems (metal abundances)
(Alcock et al 2001, Lasserre et al 2000)
the only remaining hypothesis, under gaseous form,
Either hot gas in the intergalactic medium and clusters
Either cold gas in the outer parts of galaxies + filaments
(Pfenniger & Combes 94)
38
First gas structures
After recombination, GMC of 105-6Mo collapse and fragment
Up to 10-3 Mo, H2 efficient cooling
The bulk of the gas does not form stars
But a fractal structure, in equilibrium with TCMB
After the first stars, re-ionisation
The cold gas survives to be assembled in large-scale filaments
Then in galaxies
Way to resolve the « cooling catastrophe »
Moderates the gas consumption into stars
39
History since
the Big-Bang
Observations
Look back in time
Big-Bang
z=1000
Recombination 3 105yr
Dark Age
z=10
Up to 95% of the age
of the Universe
up to the horizon
1st stars, QSO 0.5109yr
Cosmic Renaissance
z=6
End of dark age
End of reionisation 109yr
Evolution of Galaxies
z=0.5
Solar System 9 109yr
40
z=0
Today 13.7 109yr
Reionisation
years
Progressive percolation of ionized zones
41
WHIM
Where are the baryons?
6% in galaxies ; 3% in galaxy clusters (X-ray gas)
~30% in Lyman-alpha forest of cosmic filaments
Shull et al 05, Lehner et al 06
5-10% in the Warm-Hot WHIM 105-106K
Nicastro et al 05, Danforth et al 06
ICM
~50% are not yet identified!
The majority of baryons are
not in galaxies
42
DM
Problems of the standard L-CDM model
Prediction of cusps in galaxy center, which are in particular
absent in dw-Irr, dominated by dark matter
Low angular momentum of baryons, and as a consequence
formation of much too small galaxy disks
 Prediction of a large number of small halos, not observed
The solution to all these problems
could come from unrealistic
baryonic physics (SF, feedback?),
or lack of spatial resolution in
simulations, or wrong nature
of dark matter?
43
Predictions LCDM: cusp versus core
Power law of density profile a ~1-1.5, observations a ~0
Dwarf Irr : DDO154 the prototype
Carignan & Beaulieu 1989
No cusp
DM Density is not
a power-law of -1/-1.5 (cusp)
But a core
Even the LSB late-type
galaxies are dominated by
baryons (stars) in their
centers
Swaters et al 2009
45
Relation between gas and dark matter
Dwarf Irr galaxies are dominated by dark matter, but also
gas mass dominates the stellar mass
Follow the relation sDM/sHI = cste
The rotation curves can be reproduced, by multiplying the
gas surface density by a constant factor (7-10)
 CDM would not dominate in the centre, as is already the case
In more evolved galaxies (early-type), dominated by stars
In the simulations, the proto-galaxies are a function of Wb
(Gardner et al 03), and the resolution of the simulations
(sub-grid physics)
46
Hoekstra et al (2001)
sDM/sHI
In average ~10
47
Rotation curves of dwarfs
DM radial distribution identical to that in HI gas
The DM/HI ratio depends slightly on type
(larger for early-types)
NGC1560
HI x 6.2
Angular momentum and disk formation
Baryons lose their angular momentum on the CDM
Usual paradigm: baryons at the start  same specific AM than DM
The gas is hot and shock heated to the Virial temperature of the halo
But another way to accrete mass is cold gas mass accretion
Gas is channeled through filaments, moderately heated by weak
shocks, and radiating quickly
Accretion is not spherical, gas keeps angular momentum
Rotation near the Galaxies, more easy to form disks
External gas accretion
Katz et al 2002:
shock heating to the dark halo
virial temperature, before cooling
to the neutral ISM temperature?
Spherical
Cold mode accretion is the most
efficient: weak shocks, weak
heating and efficient radiation
gas channeled along filaments
strongly dominates at z>1
Too many small
structures
Today, CDM simulations
predict 100 times too many
small haloes around galaxies
like the Milky Way
Disruption of small structures
More cold gas in dwarf haloes
Much less concentration
Fragmentation
LSB (Mayer et al 01)
Baryonic clumps heat DM through
dynamical friction and smooth any cusp
in dwarf galaxies
The material is more dissipative,
more resonant, and
more prone to disruption and merging
May change the mass function for
low-mass galaxies
HSB
Dark Matter in Galaxy Clusters
In clusters, the hot gas dominates the visible mass
Most baryons have become visible
fb = Wb / Wm ~ 0.15
The radial distribution dark/visible is reversed
The mass becomes more and more visible with radius
(David et al 95, Ettori & Fabian 99, Sadat & Blanchard 01)
The gas mass fraction varies from 10 to 25% according to clusters
Radial distribution of the hot gas fraction fg in clusters
The abscissa is the mean density in radius r, normalised
to the critical density (Sadat & Blanchard 2001)
Another solution for
galaxy rotation curves
Either dark matter,
But also…..
A modification of
Newton’s law
55
MOND =MOdified Newtonian Dynamics
Modification at weak acceleration
a = (a0 aN)1/2
aN ~ 1/r2  a ~ 1/r
 V2 = cste
a2 ~V4/R2 ~ GM/R2 (TF)
(Milgrom 1983)
aN = a m (x)
x = a/a0 a0 = 1.2 10-10 m/s2 or 1 Angstroms/s2
x << 1 Mondian regime m(x)  x
x>>1 Newtonian
m(x)  1
56
Tully-Fisher relation
for gaseous galaxies
works much better in
adding gas mass
Relation Mbaryons
with Rotational V
Mb ~ Vc4
McGaugh et al (2000)  Baryonic Tully-Fisher
57
Multiple rotation curves..
Sanders & Verheijen 1998, all types, all masses
--- gas, …. Stellar disk, _ _ _ bulge
58
Problems of MOND in galaxy clusters
Inside galaxy clusters, there still existing some missing mass,
which cannot be explained by MOND, since the cluster center
is only moderately in the MOND regime (~0.5 a0)
Observations in X-rays: hot gas in hydrostatic equilibrium,
and weak gravitational lenses (shear)
MOND reduces by a factor 2 the missing mass
It remains another component, which could be neutrinos….
(plus baryons)
The baryon fraction is not the universal one in clusters
(so baryons could still exist in the standard LCDM model)
But if CDM does not exist, there is no limiting fraction
59
MOND & galaxy clusters
According to baryon physics, cold gas could accumulate at the cluster
centers
Alternatively, neutrinos could represent 2x more mass than the
baryons
60
The bullet cluster
Proof of the existence of non-baryonic
matter
X-ray gas
Total mass
Accounted for in MOND + neutrinos (2eV, Angus et al 2006)
61
Mahdavi et al 2007
Abell 520
z=0.201
Red= X-ray gas
Contours= lensing
Massive DM core
Coinciding with X gas
but devoid of galaxies
Cosmic train wreck
Opposite case!
62
Abell 520 merging clusters
Contours=total mass
Contours = X-ray gas
How are the galaxies ejected from the CDM peak??
63
Jee et al 2007
CL 0024+17
Contours=lensing
Contours= X-ray
64
Cosmic ring of DM, CL0024+17
65
Cold accretion on galaxies
Conventional scenario: shock heating to the Virial temperature
(106 K for a MW-type galaxy)
While simulations with enough resolution show 2 modes of accretion
Cold gas falling along filaments, the fraction of cold gas being
larger in low-mass haloes (MCDM < 3 1011 Mo)
Keres et al
2005
66
Cold gas inflow in filaments
Temperature
Density of the cold gas
Quenching of star formation
Origin of bimodality?
Dekel & Birnboim (2006)
67
Feedback due to Starburst or AGN
Di Matteo et al 2005
68
Perseus Cluster
Salomé et al 2006
Fabian et al 2003
69
Conclusion
Parameters of the Univers: Wm=0.24, with 15% baryons, 85% ??
The standard dark matter model CDM, with L = 0.76 is the best fit
to observations, and predict beautifully the large-scale structures
There remain problems at galactic scales:
 CDM is predicted to dominate at galaxy centers with cusps
Angular momentum problem for baryons, lost to the
benefit of CDM, disk formation problem
Prediction of too many small halos, not observed
The baryonic physics could solve part of the problems
And in particular cold gas accretion
70
Or else modification of gravity?