1. Galaxy Formation James Binney Oxford University TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: AAA A A A A

2. Outline Cosmological clustering Cosmological clustering Scales introduced by baryons Scales introduced by baryons Timeline Timeline Chemical evolution Chemical evolution Cores of Es Cores of Es Cooling flows Cooling flows

3. CDM Background Power spectrum of fluctuations Power spectrum of fluctuations ! filaments+voids ! filaments+voids ! hierarchy of halos ! hierarchy of halos Analytic model: Extended Press-Schechter theory Analytic model: Extended Press-Schechter theory characteristic mass(z) characteristic mass(z) Halo characteristic velocity(M) Halo characteristic velocity(M) Halo mass fn Halo mass fn Halo merger prob Halo merger prob

4. Primary & secondary halos Secondary halo: one that has fallen in to another halo Secondary halo: one that has fallen in to another halo Survival time t fric ' t dyn (M/m) Survival time t fric ' t dyn (M/m) Primary halo: one that hasn’t fallen in Primary halo: one that hasn’t fallen in P-S theory applies only to primary halos P-S theory applies only to primary halos Older theory didn’t believe in secondary halos Older theory didn’t believe in secondary halos Primary/Secondary status changes sign of gas accretion/depletion Primary/Secondary status changes sign of gas accretion/depletion

5. And baryons? Have e.m. interactions: Have e.m. interactions: Short-range scattering Short-range scattering –adiabatic/shock compressive heating Exchange E with e.m. waves Exchange E with e.m. waves –emission of bremsstrahlung + line radiation; –photo + Compton heating Can form stars and BHs, which heat surrounding matter Can form stars and BHs, which heat surrounding matter –Mechanically (winds/jets/shocks) –photonically

6. Characteristic numbers Photo-heating Photo-heating –T ' 10 4 K $ c s ' 10 km/s $ M=10 8 M ¯ SN heating SN heating –With Salpeter IMF get 1 SN / 200 M ¯ of SF ! E SN =10 44 J of mechanical E –T max =(m p /200M ¯ )E SN /k B =3 £ 10 7 K

7. Numbers (cont) Gravitational heating Gravitational heating –Rate of grav heating/unit mass H grav =(GM H /r 2 )v=G ½ rv H grav =(GM H /r 2 )v=G ½ rv –Rate of radiative cooling/unit mass C rad = ¤ (T)n 2 /(nm p )= ¤½ B /m p 2 C rad = ¤ (T)n 2 /(nm p )= ¤½ B /m p 2 ¤ (T) = ¤ (T 0 )(T/T 0 ) 1/2 = ¤ (T 0 )v/v 0 with T 0 ' 10 6 K, v 0 = 100 km/s ¤ (T) = ¤ (T 0 )(T/T 0 ) 1/2 = ¤ (T 0 )v/v 0 with T 0 ' 10 6 K, v 0 = 100 km/s C rad = ¤ (T 0 )f B ½ v/(v 0 m p 2 ) with f B =0.17 C rad = ¤ (T 0 )f B ½ v/(v 0 m p 2 ) with f B =0.17 –H grav /C rad = Gm p 2 v 0 r/f B ¤ (T 0 ) = r/r crit where r crit =160kpc – ! M crit ' 10 12 M ¯ Bottom line: smaller systems never get hot Bottom line: smaller systems never get hot Galaxies don’t form by cooling Galaxies don’t form by cooling

8. Timeline z ' 20: small-scale (M~10 6 M ¯ ) structures begin to collapse z ' 20: small-scale (M~10 6 M ¯ ) structures begin to collapse Location: where long & short waves at crests, ie what will be centres of rich clusters Location: where long & short waves at crests, ie what will be centres of rich clusters Voids shepherd matter into filaments Voids shepherd matter into filaments Larger & larger regions collapse, driving mergers of substructures Larger & larger regions collapse, driving mergers of substructures Voids merge too Voids merge too A substructures survives if it falls into sufficiently bigger halo A substructures survives if it falls into sufficiently bigger halo Action spreads from densest to less dense regions (“downsizing”) Action spreads from densest to less dense regions (“downsizing”) Initially Universe extremely cold (T<1K) Initially Universe extremely cold (T<1K) At z ' 6 photo heated to 10 4 K At z ' 6 photo heated to 10 4 K Halos less massive than 10 8 M ¯ subsequently can’t retain gas Halos less massive than 10 8 M ¯ subsequently can’t retain gas In low-density regions ! large population dark-dark halos? In low-density regions ! large population dark-dark halos?

9. Timeline (contd) At any location scale of halo formation increases, as does T vir At any location scale of halo formation increases, as does T vir Until T vir =10 6 K, M=10 12 M ¯ SN-heated gas escapes Until T vir =10 6 K, M=10 12 M ¯ SN-heated gas escapes Until T vir =10 6 K, M=10 12 M ¯ infalling gas cold Until T vir =10 6 K, M=10 12 M ¯ infalling gas cold Halos with M>10 12 M ¯ acquire hot atmospheres Halos with M>10 12 M ¯ acquire hot atmospheres Heating by AGN counteracts radiative cooling Heating by AGN counteracts radiative cooling Hot gas evaporates limited cold infall ! “quenching” of SF Hot gas evaporates limited cold infall ! “quenching” of SF

10. Chemical evolution Closed-box model Closed-box model Z=M h /M g (Z ¯ =0.02) Z=M h /M g (Z ¯ =0.02) Instantaneous recycling Instantaneous recycling ± M h = p ± M s -Z ± M s = (p-Z) ± M s ± M h = p ± M s -Z ± M s = (p-Z) ± M s ± Z = ± (M h /M g ) = ( ± M h -Z ± M g )/M g ± Z = ± (M h /M g ) = ( ± M h -Z ± M g )/M g Eliminate ± M h ! ± Z = -p ± ln(M g ) Eliminate ± M h ! ± Z = -p ± ln(M g ) ! Z(t)=-p ln[M g (t)/M g (0)] ! Z(t)=-p ln[M g (t)/M g (0)] Ok for gas-rich dwarfs but not dSph! Ok for gas-rich dwarfs but not dSph! M s [<Z(t)]=M s (t)=M g (0)-M g (t)=M g (0)(1-e -Z/p ) M s [<Z(t)]=M s (t)=M g (0)-M g (t)=M g (0)(1-e -Z/p ) M s (< ® Z)/M s (<Z)=(1-x ® )/(1-x) where x=M g (t)/M g (0) M s (< ® Z)/M s (<Z)=(1-x ® )/(1-x) where x=M g (t)/M g (0) G-dwarf problem: with x=0.1 M s (<Z ¯ /4) ' 0.49M s but only 2% stars <0.25Z ¯ G-dwarf problem: with x=0.1 M s (<Z ¯ /4) ' 0.49M s but only 2% stars <0.25Z ¯

11. In or out? The box is open! The box is open! Outflow or inflow? Outflow or inflow? Arguments for inflow: Arguments for inflow: –SFR ' const in solar nhd (Hipparcos) –S0 galaxies are spirals that have ceased SF (TF relation & specific GC frequency); they are also in locations where we expect inflow to have been reversed (Bedregal et al 2007) Arguments for outflow: Arguments for outflow: –in rich clusters ~half of heavy elements are in IGM –in M82 you see ouflow (probably in Galaxy too) –application of leaky box to globular-cluster system

12. Leaky-box model dM t /dt=-c dM s /dt dM t /dt=-c dM s /dt ! ! Can also apply to centres of ellipticals with c( ¾ ) by equating E of ejection to E SN (S5.3.2 of Binney & Merrifield) Can also apply to centres of ellipticals with c( ¾ ) by equating E of ejection to E SN (S5.3.2 of Binney & Merrifield)

13. ® enhancement Most “ ® elements” (O, Ne, Mg, Si, S, A, Ca) ejected by core-collapse SNe; ¿ ~10Myr Most “ ® elements” (O, Ne, Mg, Si, S, A, Ca) ejected by core-collapse SNe; ¿ ~10Myr Majority of Fe injected by type 1a SNe; ¿ ~1Gyr Majority of Fe injected by type 1a SNe; ¿ ~1Gyr Spheroids (metal-poor halo) ® enhanced (relative to Sun) Spheroids (metal-poor halo) ® enhanced (relative to Sun) Implies SF complete inside 1Gyr Implies SF complete inside 1Gyr

14. Centres of Es Photometry of Es fitted by Photometry of Es fitted by Lauer + 07 Nipoti & Binney 07 Conclude: on dry merging cores destroyed by BHs; in gas-rich mergers reformed by SF

15. Cooling flows: mass dropout In 1980s & 90s X-ray profiles interpreted on assumption that (i) steady-state, (ii) no heating In 1980s & 90s X-ray profiles interpreted on assumption that (i) steady-state, (ii) no heating Imply diminishing flow to centre Imply diminishing flow to centre ICM multiphase (Nulsen 86) ICM multiphase (Nulsen 86) Field instability analysis implied runaway cooling of overdense regions (t cool / 1/  ) Field instability analysis implied runaway cooling of overdense regions (t cool / 1/  ) Cooler regions radiate all E while at r À 0 Cooler regions radiate all E while at r À 0 Predicts that there should be (a) cold gas and (b) line radiation from T<10 6 K throughout inner cluster Predicts that there should be (a) cold gas and (b) line radiation from T<10 6 K throughout inner cluster Stewart et al 84

16. G modes Malagoli et al (87): overdense regions just crests of gravity waves Malagoli et al (87): overdense regions just crests of gravity waves In half a Brunt-Vaisala period they’ll be underdensities. In half a Brunt-Vaisala period they’ll be underdensities. Oscillations weakly overstable ( Balbus & Soker 89 ) but in reality probably damped. Oscillations weakly overstable ( Balbus & Soker 89 ) but in reality probably damped. Conclude: over timescale <t cool heating must balance radiative losses Conclude: over timescale <t cool heating must balance radiative losses Systems neither cooling nor flowing! Systems neither cooling nor flowing!

17. 2001 – Chandra & XMM-Newton XMM doesn’t see lines of <10 6 K gas XMM doesn’t see lines of <10 6 K gas XMM shows that deficit of photons at <1keV not due to internal absorption XMM shows that deficit of photons at <1keV not due to internal absorption But associated with “floor” T ' T vir /3 But associated with “floor” T ' T vir /3 Chandra shows that radio plasma has displaced thermal plasma Chandra shows that radio plasma has displaced thermal plasma (Bohringer et al 02) (Peterson et al 02)

18. Outward increasing entropy Omma thesis 05 Donahue 04

19. Summary (cooling flows) Hot atmospheres not thermally unstable: will cool first @ centre Hot atmospheres not thermally unstable: will cool first @ centre Clear evidence that weak radio sources associated with BH keep atmospheres hot Clear evidence that weak radio sources associated with BH keep atmospheres hot Mechanism: probably Bondi accretion at rate controlled by central density Mechanism: probably Bondi accretion at rate controlled by central density Result: halos M>10 12 M ¯ have little SF Result: halos M>10 12 M ¯ have little SF Smaller halos that fall into such big halos gradually sterilized by ablation too Smaller halos that fall into such big halos gradually sterilized by ablation too Hence decline in cosmic SF rate at current epoch Hence decline in cosmic SF rate at current epoch

20. Papers to read Dekel & Silk 1986 Dekel & Silk 1986 Frenk & White 1991 Frenk & White 1991 Benson et al 2003 Benson et al 2003 Cattaneo et al 2006 Cattaneo et al 2006