Formation of Galaxies

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Formation of Galaxies

• Dynamics of Galaxies
• Françoise COMBES

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Amas et superamas proches
Large-scale structures in Local Universe
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Gott et al (03) Conformal map Logarithmic Great
Wall SDSS 1370 Mpc 80 longer than CfA2 Great
Wall
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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)
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2dF Galaxy Redshift Survey
250 000 galaxies, Colless et al (2003)
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Comparaison between CfA2 SDSS (Gott 2003)
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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 ltlt 1
definition dr /r d
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free-fall time tff (G r 1) -1/2 Expansion
time-scale texp (G lt r gt) -1/2 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) ?T/T 10-5 at
large scale
Structures grow following the universe characteris
tic radius d R(t) (1 z)-1
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Expansion of Universe redshift
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The sky is uniform at l3mm 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
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Universe homogeneous isotrope until
the recombination and the collapse of structures
Last scattering surface Epoch of t380 000
yrs Anisotropies measured in the
cosmological background radiation
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WMAP Results
Wm 0.26 L 0.74 Wb 0.04 Ho 71km/s/Mpc Age
13.7 Gyr Flat Universe
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The parameters of the Universe
Anisotropies of the CMB
Observations of SN Ia Gravitationnal lenses
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A simple perturbation
Creates a depression ? Sound wave at c /v3
Sound Horizon at recombination R150Mpc
Galaxies in over-densities ? Acoustic waves
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Multiple perturbations
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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 gt z eq
z lt zeq Radiation
Matter l gt ct ? (1
z) -2 ? (1 z) -1 l lt ct ? cste ?
(1 z) -1
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r R-3 matter r R-4 photons
Point of Equivalence E
Time ?
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Growth of adiabatic fluctuations At scales of
1014Mo (8 Mpc) They grow until they contain
the horizon mass Then stay constant (calibration
t0, 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
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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 ?r /r ?M/M A M-a a
2/3, ou ?(k)2 P(k) kn avec n1 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
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Fluctuations of density
Tegmark et al 2004
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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 µ
size -a with a 1.7 Benoît Mandelbrot in
1975 invents the name fractal extension at
the Universe Regularity emerges from the random
distributions
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Galaxy catalogue CfA 2
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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
(W1) 10-29 g/cm3
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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 ) µ r-g On the figure, slope g -1
Corresponding to D 2 M ( r ) r2
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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)
dk2 P(k) kn, with n1 At large scales n -3
at small scales tilt when ?r ?m At the horizon
scale dM/M M-1/2 -n/6 when n gt -3,
hierarchical formation (dM/M ) Abel Haiman 00
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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 µ R2 r µ 1/R
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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)
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Gas
Dark matter CDM
Galaxies
Simulations (Kauffmann et al)
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• 4  phases 
• 4 Zoom levels
• from 20 to 2.5 Mpc.
• z 3. (from. z10.)

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Multi-zoom Technique

• Objective
• Evolution of a galaxy
• (0.1 to 10 kpc)
• Accretion of gas
• (10 Mpc)

Semelin Combes 2003
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Galaxies and Filaments
Multi-zoom
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Baryonic acoustic peaks
Wavess detected today In the distribution of
baryons 50 000 galaxies SDSS
Eisenstein et al 2005
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Baryonic Oscillations a standard ruler
Alcock Paczynski (1979) Test of cosmological
constant Can test the bias b Galaxies/dark matter

• Eisenstein et al. (2005)
• 50 000 galaxies SDSS

c Dz/H Dq D ?Possibility to determine H(z)
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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?
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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
?No detection up to now
Direct
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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)
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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

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History since the Big-Bang
Big-Bang Recombination 3 105yr Dark Age
1st stars, QSO 0.5109yr Cosmic Renaissance
End of dark age End of reionisation
109yr Evolution of Galaxies Solar System 9
109yr Today 13.7 109yr
z1000
Observations Look back in time Up to 95 of the
age of the Universe ?up to the horizon
z10
z6
z0.5
z0
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Reionisation
Progressive percolation of ionized zones
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Where are the baryons?
WHIM

• ?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
• 50 are not yet identified!
• The majority of baryons are
• not in galaxies

ICM
DM
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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?

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Predictions LCDM cusp versus core
Power law of density profile a 1-1.5,
observations a 0
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Dwarf Irr DDO154 the prototype
DM Density is not a power-law of -1/-1.5
(cusp) But a core
Carignan Beaulieu 1989 ?No cusp
Even the LSB late-type galaxies are dominated
by baryons (stars) in their centers
Swaters et al 2009
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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)
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Hoekstra et al (2001)
sDM/sHI
In average 10
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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
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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
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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
zgt1
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Too many small structures
Today, CDM simulations predict 100 times too
many small haloes around galaxies like the Milky
Way
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Disruption of small structures
More cold gas in dwarf haloes Much less
concentration ?Fragmentation 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
LSB (Mayer et al 01)
HSB
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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
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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)
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Another solution forgalaxy rotation curves
Either dark matter, But also.. A modification
of Newtons law
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MOND MOdified Newtonian DynamicsModification 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 ltlt
1 Mondian regime m(x) ? x xgtgt1 Newtonian
m(x) ? 1
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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
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Multiple rotation curves..
Sanders Verheijen 1998, all types, all
masses --- gas, . Stellar disk, _ _ _ bulge
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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

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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

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The bullet cluster
X-ray gas
Proof of the existence of non-baryonic
matter Accounted for in MOND neutrinos (2eV,
Angus et al 2006)
Total mass
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Abell 520z0.201
Mahdavi et al 2007

• Red X-ray gas
• Contours lensing
• Massive DM core
• Coinciding with X gas
• but devoid of galaxies
• Cosmic train wreck
• Opposite case!

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Abell 520 merging clusters
Contourstotal mass Contours X-ray
gas How are the galaxies ejected from the CDM
peak??
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CL 002417
Jee et al 2007
Contourslensing
Contours X-ray
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Cosmic ring of DM, CL002417
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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 lt 3 1011 Mo)
Keres et al 2005
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Cold gas inflow in filaments
Temperature
Density of the cold gas
Quenching of star formation Origin of bimodality?
Dekel Birnboim (2006)
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Feedback due to Starburst or AGN
Di Matteo et al 2005
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Perseus Cluster
Salomé et al 2006
Fabian et al 2003
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Conclusion

• Parameters of the Univers Wm0.24, 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
• Or else modification of gravity?