Formation of Galaxies

1. Formation of Galaxies Dynamics of Galaxies Françoise COMBES

2. Large-scale structures in Local Universe Amas et superamas proches

3. Gott et al (03) Conformal map Logarithmic Great Wall SDSS 1370 Mpc 80% longer than CfA2 Great Wall

4. 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)

6. 2dF Galaxy Redshift Survey 250 000 galaxies, Colless et al (2003)

7. Comparaison between CfA2 & SDSS (Gott 2003)

8. 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

9. free-fall time tff = (G r1) -1/2 Expansion time-scale texp = (G < r >) -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 ~ 10-5at large scale Structures grow following the universe characteristic radius d ~ R(t) ~ (1 + z)-1

10. Expansion of Universe & redshift

11. 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

12. 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

13. WMAP Results Wm = 0.26 L = 0.74 Wb =0.04 Ho = 71km/s/Mpc Age = 13.7 Gyr Flat Universe

14. The parameters of the Universe Anisotropies of the CMB Observations of SN Ia Gravitationnal lenses

15. A simple perturbation Creates a depression  Sound wave at c /√3 Sound Horizon at recombination R~150Mpc Galaxies in over-densities  Acoustic waves

16. Multiple perturbations

17. 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 z < zeq Radiation Matter l > ct  ~(1 + z) -2  ~(1 + z) -1 l < ct ~ cste  ~(1 + z) -1

18. NEUTRAL Radiation r Matter IONISED 104 z 103 r ~ R-3 matter r ~ R-4 photons Point of Equivalence E Time 

19. 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

20. 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 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

21. Fluctuations of density Tegmark et al 2004

22. 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

23. Galaxy catalogue CfA 2

24. Density of structures in the Universe Solar System 10-12 g/cm3 Milky Way10-24 g/cm3 Local Group 10-28 g/cm3 Galaxy clusters10-29 g/cm3 Super-cluster 10-30 g/cm3 Density of photons (3K)10-34 g/cm3 Critical density (W=1) 10-29 g/cm3

25. 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

26. 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

27. 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

28. 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)

30. Gas Dark matter CDM Galaxies Simulations (Kauffmann et al)

31. 4 « phases » 4 Zoom levels from 20 to 2.5 Mpc. z = 3. (from. z=10.)

32. Multi-zoom Technique Objective: • Evolution of a galaxy (0.1 to 10 kpc) • Accretion of gas (10 Mpc) Semelin & Combes 2003

33. Galaxies and Filaments Multi-zoom

34. Baryonic acoustic peaks Wavess detected today In the distribution of baryons 50 000 galaxies SDSS Eisenstein et al 2005

35. cDz/H Observer DqD 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 cDz/H = DqD Possibility to determine H(z)

36. 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?

37. 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

38. 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)

39. 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

40. Big-Bang Recombination3 105yr Dark Age 1st stars, QSO 0.5109yr Cosmic Renaissance End of dark age End of reionisation109yr Evolution of Galaxies Solar System 9 109yr Today 13.7 109yr z=1000 History since the Big-Bang Observations Look back in time Up to 95% of the age of the Universe up to the horizon z=10 z=6 z=0.5 z=0

41. years Reionisation Progressive percolation of ionized zones

42. 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 • ~50% are not yet identified! The majority of baryons are not in galaxies ICM DM

43. 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?

44. Predictions LCDM: cusp versus core Power law of density profile a ~1-1.5, observations a ~0

45. 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

46. 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)

47. Hoekstra et al (2001) sDM/sHI In average ~10

48. 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

49. 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

50. 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