Post on 18-Jan-2016
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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 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?