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 mapLogarithmic

Great Wall SDSS1370 Mpc

80% longer thanCfA2 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 spectraimages of 100 millions objects, 100 000 Quasars1/4 of sky surface (2.5m telescope)Apache Point Observatory (APO), Sunspot, New Mexico, USA

2dF GRS: Galaxy Redshift Surveys: 250 000 galaxy spectraAAT-4m, Australia et UK (400 spectra simultaneously)

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2dF Galaxy Redshift Survey

250 000 galaxies, Colless et al (2003)

7Comparaison 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 collapseexponentially, but develop in a linear manner

du/dt +(u grad)u = -grad -1/ grad p; d /dt + div u =0 = 4 G

Initial density fluctuations / << 1 definition / =

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free-fall time tff = (G 1) -1/2

Expansion time-scale texp = (G < >) -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 universecharacteristic radius ~ R(t) ~ (1 + z)-1

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Expansion of Universe & redshift

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The sky is uniform at =3mm

Once the constant level subtracted dipole ( V = 600km/s)

After subtraction of the dipole, The Milky Way, emissionof the dust, synchrotron, etc..

Subtraction of the Milky Way Random fluctuations

T/T ~ 10-5

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Universe homogeneous & isotrope until therecombination and thecollapse of structures

Last scattering surface Epoch of t=380 000 yrs

Anisotropies measuredin the cosmologicalbackground radiation

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WMAP Results

m = 0.26 = 0.74b =0.04Ho = 71km/s/Mpc

Age = 13.7 GyrFlat Universe

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The parameters of the Universe

Anisotropies of the CMB

Observations of SN IaGravitationnal lenses

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Creates a depression

Sound wave at c /√3 Sound Horizon at recombination

R~150Mpc

Galaxies

in over-densities

Acoustic waves

A simple perturbation

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Multiple perturbations

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Only the non-baryonic matter, which particles do not interactwith 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 allscales after equality, but grow only perturbations of scale larger than the horizon before equality (free streaming)

z > z eq z < zeq

Radiation Matter

> ct ~(1 + z) -2 ~(1 + z) -1

< ct ~ cste ~(1 + z) -1

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104 z 103

NEUTRAL

Radiation

Matter

IONISED

~ R-3 matter ~ 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 t=0, arrow)

The matter fluctuations (…) "standard model" followthe radiation, and grow only after the Recombination R The CDM fluctuations grow from the point Eequivalence matter -radiation

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Power spectrumTheory of inflation: One suppose the spectrum scale independent,And the power law such that the perturbations always enter thehorizon with the same amplitude

/ ~ M/M = A M-a

a = 2/3, ou (k)2 = P(k) = kn avec n=1

P(k) ~k at large scalebut P(k) tilted n= -3At small scale (Peebles 82)

Comes from the streaming effect For scales below the horizon

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Fluctuations of density

Tegmarket al 2004

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Fractales and Structure of the Universe

Galaxies are not distributed homogeneously on the skybut along filaments, following a hierarchyGalaxies 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 - with = 1.7

Benoît Mandelbrot in 1975: invents the name « fractal » extension at the UniverseRegularity 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 (=1) 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

( r ) r-

On the figure, slope = -1 Corresponding to D = 2

M ( r ) ~ r2

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Hierarchical FormationIn 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)

| k|2 =P(k) ~ kn, with n=1At large scalesn= -3 at small scalestilt when ρr ~ ρm

At the horizon scale

M/M ~M-1/2 -n/6

when n > -3, hierarchicalformation (M/M )Abel & Haiman 00

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Hierarchical galaxyformation

The smallest structures form first, with the typical sizes ofdwarf galaxies or globular clusters

By successive mergers and accretion more and ore massive systemsform

They are less and less dense (expansion)

M R2 & 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 accountthrough semi-analytic models, à la Press-Schechter)

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Dark matter CDM

Gas

GalaxiesSimulations(Kauffmann et al)

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4 « phases »

4 Zoom levels

from 20 to 2.5 Mpc.

z = 3. (from. z=10.)

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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

Eisenstein et al 2005

Wavess detected todayIn the distribution of baryons

50 000 galaxies SDSS

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Baryonic Oscillations: a standard ruler

Observer

c z/H = D

Possibility to determine H(z)

D

c z/H

Alcock & Paczynski (1979)Test of cosmological constant

Can test the bias bGalaxies/dark matter

Eisenstein et al. (2005)50 000 galaxies SDSS

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Hypotheses for the CDM particles

Particles which are no longer relativistic at decoupling: COLDParticles WIMPS (weakly interactive massive particles)

Neutralino: the lightest supersymmetric particle LSPRelic of the Big-Bang, should disintegrate in gamma rays(40 Gev- 5Tev)

May be lighter particles, or with more non-gravitationnalinteraction? (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 searchesCould 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)

Direct

Indirect

No detection up to now

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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 experimentsor 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 clustersEither 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 starsBut 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 ageEnd of reionisation 109yr

Evolution of Galaxies

Solar System 9 109yr

Today 13.7 109yr

Observations Look back in time

Up to 95% of the ageof the Universeup to the horizon

z=10

z=1000

z=6

z=0

z=0.5

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Reionisation

Progressive percolation of ionized zones

years

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Where are the baryons?

6% in galaxies ; 3% in galaxy clusters (X-ray gas)

~30% in Lyman-alpha forest of cosmic filamentsShull et al 05, Lehner et al 06

5-10% in the Warm-Hot WHIM 105-106KNicastro et al 05, Danforth et al 06

~50% are not yet identified!

The majority of baryons are not in galaxies

WHIM

ICM

DM

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Problems of the standard -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?

Predictions LCDM: cusp versus core

Power law of density profile ~1-1.5, observations ~0

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Dwarf Irr : DDO154 the prototype

Even the LSB late-type galaxies are dominated bybaryons (stars) in their centers

Swaters et al 2009

Carignan & Beaulieu 1989No cusp

DM Density is not a power-law of -1/-1.5 (cusp)But a core

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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 DM/HI = cste

The rotation curves can be reproduced, by multiplying thegas surface density by a constant factor (7-10)

CDM would not dominate in the centre, as is already the caseIn more evolved galaxies (early-type), dominated by stars

In the simulations, the proto-galaxies are a function of b

(Gardner et al 03), and the resolution of the simulations(sub-grid physics)

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Hoekstra et al (2001)

DM/HI

In average ~10

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 DMThe 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 momentumRotation near the Galaxies, more easy to form disks

External gas accretion

Katz et al 2002:

shock heating to the dark halovirial temperature, before coolingto the neutral ISM temperature?Spherical

Cold mode accretion is the mostefficient: weak shocks, weakheating and efficient radiation

gas channeled along filamentsstrongly dominates at z>1

Too many small structures

Today, CDM simulations predict 100 times too manysmall haloes around galaxieslike the Milky Way

Disruption of small structures

More cold gas in dwarf haloesMuch less concentrationFragmentation

Baryonic clumps heat DM throughdynamical friction and smooth any cuspin dwarf galaxies

The material is more dissipative, more resonant, andmore prone to disruption and merging

May change the mass function for low-mass galaxies

LSB (Mayer et al 01)

HSB

Dark Matter in Galaxy Clusters

In clusters, the hot gas dominates the visible massMost baryons have become visible

fb = b / m ~ 0.15

The radial distribution dark/visible is reversedThe 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 clustersThe abscissa is the mean density in radius r, normalisedto the critical density (Sadat & Blanchard 2001)

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Another solution forgalaxy rotation curves

Either dark matter,

But also…..

A modification of Newton’s 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 (x)x = a/a0 a0 = 1.2 10-10 m/s2 or 1 Angstroms/s2

x << 1 Mondian regime (x) xx>>1 Newtonian (x) 1

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McGaugh et al (2000) Baryonic Tully-Fisher

Tully-Fisher relationfor gaseous galaxiesworks much better inadding gas mass

Relation Mbaryons

with Rotational V

Mb ~ Vc4

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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 centeris 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 massIt 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 CDM 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 thebaryons

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The bullet cluster X-ray gas

Total massProof of the existence of non-baryonic matter

Accounted for in MOND + neutrinos (2eV, Angus et al 2006)

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Abell 520z=0.201

Mahdavi et al 2007

Red= X-ray gasContours= lensingMassive DM coreCoinciding with X gasbut devoid of galaxies

Cosmic train wreck

Opposite case!

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Abell 520 merging clusters

Contours=total mass Contours = X-ray gas

How are the galaxies ejected from the CDM peak??

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CL 0024+17Jee et al 2007

Contours=lensing

Contours= X-ray

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Cosmic ring of DM, CL0024+17

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Cold accretion on galaxiesConventional 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 al2005

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Cold gas inflow in filamentsDensity of the cold gas

Temperature

Dekel & Birnboim (2006)

Quenching of star formation Origin of bimodality?

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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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ConclusionParameters of the Univers: m=0.24, with 15% baryons, 85% ??

The standard dark matter model CDM, with = 0.76 is the best fitto observations, and predict beautifully the large-scale structures

There remain problems at galactic scales:

CDM is predicted to dominate at galaxy centers with cuspsAngular momentum problem for baryons, lost to the benefit of CDM, disk formation problemPrediction of too many small halos, not observed

The baryonic physics could solve part of the problemsAnd in particular cold gas accretion

Or else modification of gravity?