The physics of galaxy formation. P. Monaco, University of Trieste & INAF-OATs

Transcription

1 The physics of galaxy formation P. Monaco, University of Trieste & INAF-OATs PhD School of Astrophysics Francesco Lucchin June 2013

2 LambdaCDM model Cosmic microwave background Large-scale structure Galaxy clusters & gravitational lensing Distant supernovae Inter-galactic medium

3 Cosmology gravitational collapse z=5.7 (t=1.0 Gyr) Dark matter z=1.4 (t=4.7 Gyr) z=0 (t=13.6 Gyr) gastrophysics Galaxies Springel et al. 2006

4 Theoretical tools (within the LambdaCDM cosmogony) Semi-analytic models N-body + hydrodynamical simulations Halo Occupation Distribution models Abundance matching models

5 The physics of galaxy formation 1. Dark matter

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7 Dark-matter halos Density profile: Navarro, Frenk & White (1997, ApJ 490, 493) const 2 cx(1+cx) rh r r c, x, cx= rs rh rs ρ (rh )=200ρc (z ) ρ (r )=ρc (z)

8 Mass function of DM halos Warren et al. (2006, ApJ 646, 881)

9 Merger trees Lacey & Cole (1993, MNRAS 262, 627)

10 dynamical friction tidal stripping tidal shocks/harrassment orbit decay (merging) binary mergers

11 Dynamical friction Coulomb logarithm d v = dt orb 4 G 2 ln M sat host v orb t merge =1.17 v orb v 3orb f df M orb host ln M sat Parameter Orbital parameter Boylan-Kolchin, Ma & Quataert (2008, MNRAS, 383, 93)

12 The physics of galaxy formation 1. Dark matter 2. Shock heating and cooling

13 Gas infall into DM halos vinfall V c= GM / R 3 4 T igm K vinfall cs => shock heating to the virial T

14 Shock heating and cold flows t cool t dyn Massive halos (>1012 Msun): cooling is slower than infall gas is shock- heated at Tvir and is in roughly hydrostatic equilibrium t cool t dyn Small halos (<1011 Msun): cooling is faster than infall cold gas falls directly to the centre the shock energy is quickly dissipated White & Frenk (1991, ApJ 379, 52), Keres et al. (2005, MNRAS 363, 2), Dekel & Birnboim (2006, MNRAS 368, 2)

15 Galaxy clusters show such hot gas

16 Hot baryons in DM halos = crit c r / r s 1 r /r s NFW profile for the total mass 2 halo concentration c=r h /r s dp g M r = G g 2 dr r hydrostatic equilibrium polytropic equation of state (γp~1.2) p P g g g r = g0 [ ln 1 r /r s 1 a 1 r /r s a=a T g0 /T vir, p, c ] 1/ p 1 solution for the density Komatsu & Seljak (2001, MNRAS 327, 1353)

17 Radiative cooling of an optically thin plasma: primordial composition Katz, Weinberg & Hernquist (1996, ApJS, 105, 19) L=n i ne, T d ln T t cool= dt 1 E th 3 nkt = = L 2 ne ni Assumptions: collisional ionisation equilibrium thermal distribution of e- and ions no external ionising radiation log T (K)

18 Radiative cooling in presence of UV heating z=2, average density 1000 times average

19 Radiative cooling of an optically thin plasma: solar abundance ratios (1993, ApJS, 88, 253) metal lines dominate cooling Log T (K)

20 The "classical" cooling model in SAMs The cooling radius: r cool t : t cool r =t Bertschinger's (1989) self-similar solutions: M cool 4 g r cool r 2 cool dr cool dt The "classical" cooling model (White & Frenk 1991): M cool =4 g r cool r 2 cool Total cooling time of a mass element: dr cool dt t total : T t total T t=0 The classical model implies that: t cool r =t total r

21 The physics of galaxy formation 1. Dark matter 2. Shock heating and cooling 3. Star formation

22 Star formation and Jeans mass E tot MJ GM 3 = U +Ω = kt 2 μ mp R ( ) ( T M J K Warm phase Cold phase Molecular phase 3/ 2 n 1 cm 3 ) 2 J 1 / 2 M sun =0

23 4 Cooling below 10 K fraction of ions that are metals Maio et al. (2007, MNRAS 379, 963)

24 Star formation Kennicutt (1998, ApJ 498, 541)

25 DATA: THINGS (VLA): 21 cm -> HI BIMA-SONG + HERACLES: CO H2 SINGS (Spitzer): 24 μm GALEX: UV 24 μm + UV -> SFR resolution: 750 pc, 5.2 km/s

26 The Kennicutt relation(s) for spirals atomic molecular total Bigiel et al. (2008, AJ 136, 2846)

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28 Two relations at high redshift? Daddi et al. (2010, ApJ 714, L118)

29 The physics of galaxy formation 1. Dark matter 2. Shock heating and cooling 3. Star formation 4. Energetic feedback

30 Feedback sources 51 Supernova explosions 10 erg each >8 Msun UV from massive stars star + type Ia up to ~1050 erg each >10 Msun star Star winds AGN up to ~1050 erg each >10 Msun star 47 up to ~10 erg s for ~107 yr -1

31 SuperNova Remnant (SNR) (1) Free expansion (2) Adiabatic stage (3) Pressure-driven snowplow stage (4) Momentum conserving stage

32 SN energy feedback Energy is injected through blastwaves The ISM is heated in the adiabatic stage The ISM is cooled if the blast goes into the snowplough stage McKee & Ostriker 1977 Cioffi, McKee & Berschinger 1988 Ostriker & McKee 1988

33 The efficiency of feedback It is determined by the energy radiated away before the blast stops propagating. Blasts stop by: merging with the ISM v s=c s0 blowing out of the galaxy R s=h eff merging with other blasts Q bubbles=1

34 Feedback in DM halos thermal energy kinetic energy hot/cold gas metals

35 Feedback in DM halos outflow galactic fountain

36 Simple model of feedback (Dekel & Silk 1986) The properties of dwarf galaxies require that gas is efficiently removed from small halos. E =ϵ E M V inj aval gas Condition for removal: 2 c Energy from (tii) SNe: E aval =E SN SN M star Star formation: M star =M gas / t ff Critical Vc: V c 100 km/ s Parameters: ESN ( E51), ηsn (IMF), ε, τ (computed)

37 A simple energetic argument ϵ E SN M star 2 = M outflow vsn M star, SN vsn ϵ 750 km/s if M outflow = M star

38 The physics of galaxy formation 1. Dark matter 2. Shock heating and cooling 3. Star formation 4. Energetic feedback 5. Morphology

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40 Angular momentum of halos J = V L 3 3 a a x a x cm v d x J i = a D ijk T jl I lk t 1 / 3 M 5 /3 tidal tensor inertia tensor White (1984, ApJ 286, 38)

41 Spin parameter = E 1 / 2 J h GM 5/ 2 h V rot Vc GM h V c= rh Bett et al. (2007, MNRAS, )

42 Formation of discs Dissipation of all random motions

43 The size of discs Assuming that (1) a fraction md of the halo baryonic mass settles on the disc (2) a fraction jd of the angular momentum is conserved (3) the disc has an exponential profile (4) the disc has negligible mass Rd = G M 3/h 2 2V c E 1/ 2 r = 0 exp r Rd jd md (5) the halo has a singular isothermal profile r r 2 1 jd Rd = rh 2 md Mo, Mao & White (1998, MNRAS 295, 319)

44 Complications (1) NFW halo (2) disc mass not negligible (3) adiabatic contraction of the DM halo GM r r=const (4) central bulge Jd jd = M d md Jd = rh Jh Mh 0 V rot r r r 2 r dr V rot =V dm V d V b G Md 2 V = y [ I 0 y K 0 y I 1 y K 1 y ], Rd 2 d iterative solution! y= 1 r 2 Rd

45 Galaxy mergers

46 Bar instability Thin discs are unstable to bar formation, unless they are surrounded by a DM halo (Ostriker & Peebles 1973) Stability condition: V d Rd limit~1 G Md limit : disc is unstable to m=2 modes (Efstathiou et al. 1982, Christodoudou et al. 1995)

47 Disc instability 2 V d V d dv d 2 r =2 2 r dr r if V d ~V c then Bournaud et al. (2008, A&A 486, 741) Vc ~ 2 r cs Toomre criterion for a gas disc Q r G gas Q 1 : disc is unstable to axisymmetric modes

48 Bar instability (secular evolution) pseudo-bulges Kormeny & Kennicutt (2004, ARA&A 42, 603) Mergers bulges/ ellipticals

49 Morphology at high redshift Förster Schreiber, N. M., et al ApJ, 706, 1364

50 Problems in galaxy formation 1. Massive galaxies are red and dead

51 A problem with cooling flows in Galaxy Clusters X-ray observations of galaxy clusters allow us to estimate density and temperature, and then cooling time, of the hot gas. Peterson & Fabian (2006) Some clusters should be sites of strong cooling flows

52 ...from cooling flow clusters to cool core clusters... De Grandi & Molendi (2002, ApJ 567, 163)

53 Massive (cd) elliptical galaxies reside at the centre of galaxy clusters

54 specific star formation rate Why are massive galaxies red & dead? The mass deposited into the galaxy is 10-1 or 10-2 times that suggested by the cooling flow stellar mass Brinchmann et al. (2004, MNRAS 351, 1151)

55 Why are massive ellipticals so old? (proxy for stellar mass) Nelan et al. (2005, ApJ 632, 137)

56 A possible answer: AGN feedback Every elliptical galaxy hosts a super-massive black hole at its centre These black holes may be reactivated by the cooling gas (proxy for stellar mass) Ferrarese & Merritt 2000 Gebhardt et al. 2000

57 AGN feedback in action?

58 Problems in galaxy formation 1. Massive galaxies are red and dead 2. The stellar mass function cuts at ~1011 Msun

59 The luminosity function stellar feedback cooling time + AGN feedback Benson et al. (2003, ApJ 599, 38)

60 Constraints from abundance matching stellar feedback cooling time + AGN feedback Moster et al. (2010, ApJ 710, 903)

61 Problems in galaxy formation 1. Massive galaxies are red and dead 2. The stellar mass function cuts at ~1011 Msun 3. Galaxies show several downsizing trends

62 The many manifestations of downsizing: Fontanot et al. (2009, MNRAS 397, 1176) archaeological DS more massive galaxies host older stellar populations star formation DS: the mass of the typical SF galaxy grows with z stellar mass DS: at z 1 the number density of smaller galaxies evolves faster chemical DS: the metallicity of smaller galaxies evolves faster chemo-archaeological DS: more massive ellipticals have higher [α/fe] ratios AGN DS: the number density of fainter AGN peaks at lower z

63 Archaeological downsizing Gallazzi et al. (2005, MNRAS 362, 41)

64 Downsizing in star formation Cowie et al. (1996, AJ 112, 839)

65 Chemo-archaeological downsizing Trager et al. (2000, AJ 120, 165); Matteucci (1994, A&A 288, 57)

66 Downsizing in metallicity Maiolino et al. (2008, A&A 488, 463)

67 Downsizing in nuclear activity Brandt & Hasinger (2005, ARA&A 43, 827)

68 Stellar mass function comparison of three models: Garching-De Lucia Morgana Somerville 08 (assumed error on mass: 0.25 dex) with observational estimates of stellar mass functions by Panter+ 07, SDSS Cole+ 01, 2MASS Bell+ 03, 2MASS+SDSS Borch+ 06, COMBO17 PerezGonzalez+ 08, Spitzer Bundy+ 06, DEEP2 Drory+ 04, MUNICS Drory+ 05, FDF+GOODS Fontana+ 06, GOODS-MUSIC Pozzetti+ 07, VVDS Marchesini+ 08, 3 samples Fontanot et al. (2009)

69 in Log M* Log Stellar mass density (Msun Mpc-3) Downsizing in stellar mass

70 Lyman-break galaxies in a SAM first best-fit model second best-fit model B-drop V-drop Redshift intervals: 3.4 < z < 4.5 (B-drop) 4.5 < z < 5.5 (V-drop) 5.5 < z < 6.5 (i-drop) i-drop Lo Faro et al. (2009, A&A 399, 827)

71 Excess galaxies absolute UV magnitude: MUV~-18 star formation rate: SFR~10 Msun yr-1 apparent magnitude: z850~27 stellar mass: M*~ to bimodal metallicity: Z~solar and Z~0.25 solar hosted in halos of: Mh~ Msun with circular velocities: Vc~ km/s Important contributors to the IGM pollution Waiting for ALMA and JWST!

72 Problems in galaxy formation 1. Massive galaxies are red and dead 2. The stellar mass function cuts at ~1011 Msun 3. Galaxies show several downsizing trends 4. Growth of average SFR with z (Daddi)

73 Log average SFR of galaxies (Msun yr-1) The evolution of star formation rates Fontanot et al. (2009)

74 Problems in galaxy formation 1. Massive galaxies are red and dead 2. The stellar mass function cuts at ~1011 Msun 3. Galaxies show several downsizing trends 4. Growth of average SFR with z (Daddi) 5. Surprises from the cool side of galaxies

75 Somerville et al. (2012, MNRAS 423, 1992)

76 Sub-mm number counts with GALFORM Baugh et al. (2005, MNRAS 356, 1191)

77 Sub-mm number counts with MORGANA with a standard Salpeter IMF Fontanot et al. (2007, MNRAS 382, 903)

78 Predicted evolution of Far-IR LF Lacey et al. (2010, MNRAS 405, 2) Somerville et al. (2012, MNRAS 423, 1992)

79 Herschel-PEP Far-IR LF Gruppioni et al. (2013, MNRAS 432, 23)

80 Problems in galaxy formation 1. Massive galaxies are red and dead 2. The stellar mass function cuts at ~1011 Msun 3. Galaxies show several downsizing trends 4. Growth of average SFR with z (Daddi) 5. Surprises from the cool side of galaxies 6. Angular momentum loss in hydro simulations

81 bottom-up formation of DM halo + overcooling (White & Rees 1978, MNRAS 183, 341) + segregation of cooled baryons + dynamical friction and tidal stripping = angular momentum loss

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83 The Aquila comparison project Scannapieco et al. (2012, MNRAS 423, 1726)

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85 A successful simulation of spiral galaxy Murante et al., in preparation

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