Cooling Flows & Galaxy Formation

1. Cooling Flows & Galaxy Formation James Binney Oxford University

2. Outline • Cooling flows – historical introduction • Current issues in CF dynamics • Much work from Henrik Omma’s (05) thesis SEQUEL TOMORROW • Implications for galaxy formation and BH growth

3. “Cooling flows” • Potentials of E galaxies & galaxy clusters filled with gas @ Tvir (106 – 108 K) • Detected in Xrays since early 1970s (forman et al 72; Mitchell et al 76) • First model (Cowie & B 1977) involved mass-conserving flow to centre • Predicted jX(R) inconsistent with Einstein images Stewart et al 84

4. Distributed mass drop-out • Consistency with measured jX(r) obtained by assuming ICM multiphase (Nulsen 86) • Field instability analysis implied runaway cooling of overdense regions (tcool/ 1/) • Cooler regions radiate all E while at rÀ 0 • Predicts that there should be (a) cold gas and (b) line radiation from T<106K throughout inner cluster

5. G modes • Malagoli et al (87): overdense regions just crests of gravity waves • In half a Brunt-Vaisala period they’ll be underdensities. • Oscillations weakly overstable (Balbus & Soker 89) but in reality probably damped. • Conclude: over timescale <tcool heating must balance radiative losses • Systems neither cooling nor flowing!

6. AGN Heating • AGN natural heaters • Cooling first becomes catastrophic @ centre • Where there’s a massive BH • Accretion onto BH will be sensitive to local gas • BH could heat through (a) Compton scattering (Ciotti & Ostriker 97, 01) or (b) jets • With point-like heat source expect generation of adiabatic core • In Tabor & Binney (93) growing core matched to CF envelope • In Binney & Tabor (95) jets episodically heat gas in distributed fashion

7. 1993 - 2001 • Distributed mass dropout still regarded as established fact in mainstream (Fabian 94) • Conflicts with observation finessed with epicycles: • Internal absorption (Allen & Fabian 97) • Magnetic locking (Tribble 89, Balbus 91) • Abundance anomalies (Fabian et al 01) • Conduction from large to small r (Bertschinger & Meiksin 86, Narayan & Medvedev 01)

9. 2001 – Chandra & XMM-Newton • XMM doesn’t see lines of <106K gas • XMM shows that deficit of photons at <1keV not due to internal absorption • But associated with “floor” T' Tvir/3 • Chandra shows that radio plasma has displaced thermal plasma (Bohringer et al 02) (Peterson et al 02)

10. Bubble Models(Churazov et al 2001; Quilis et al 2001; Brueggen & Kaiser 2001,2002; Brueggen et al 2002) • Start with elliptical high-T cavity • Watch it rise • Cavity can’t be in pressure equlibrium with surroundings • The flow field around cavity dynamically important • Need for jet simulations Churazov et al 01

11. Injection Models(Quillis et al 01, Brueggen & Kaiser 02) • Add thermal energy at some fixed off-centre location • Poor representation of effects of moving jet hot-spot Brueggen & Kaiser 02

12. Jet Simulations • Early simulations 2D (Reynolds et al 02, Vernaleo 06) • Or on non-refined grids (Basson & Alexander 03) • Usually there’s a spherical boundary around the origin with free-flow condition • Omma et al (04) eliminated this boundary and had novel scheme for firing jets

13. Omma’s Simulations • Simulations on 3d hydro with adaptive grids (Bryan’s code ENZO) • Entropy (no cooling) • Density (no cooling) • Entropy (cooling) • Density (cooling) • Key processes: • 1) Uplift • 2) Mixing • 3) Excitation of non-linear gravity waves

14. Outward increasing entropy Omma thesis 05 Donahue 04

15. Current Issues 1) enough E? • Probably Quasar mode & Radio-galaxy mode depending on whether accreting cold or hot gas (Binney 04, Croton et al 06) • In RG mode L¿ LEdd and ~all output mechanical (Virgo A prime example)

16. In M87 • Chandra resolves rBondi • MBondi = 0.1 M¯/yr (Di Matteo et al 03) • So L = 5£1044 erg/s if 0.1mc2 released • LX(<20kpc) = 1043 erg/s (Nulsen & Boehringer) • LX(AGN) < 5x1040 erg/s • LMech(jet) = 1043 – 1044 erg/s (Reynolds et al 96; Owen et al 00) • So BH accreting at near MBondi & heating on kpc scales with high efficiency (Binney & Tabor 95)

17. Current Issues2) the duty cycle • AGN known to be unsteady • Energy dissipated @ centre only if jet channels have quiet time (or jets precess) (Omma & Binney 04, Vernaleo & Reynolds 06) • Sometimes two generations of bubbles (Birzan et al 04) • Suggests inter-outburst time ~ rise time ~100Myr • E of outburst > 2.5PV of bubble • Suggests Lmech ~ LX • Actually Lmech may be significantly larger

18. Define cavities by <0/4 • Evaluate PV • Peaks at only 10% of actual input Omma 05

19. Current Issues3) does mixing destroy Z gradients? • Follow tracer dye from (a) r<5kpc, and (b) 5<r<77 kpc Omma 05

20. Effect on Z gradient Omma thesis 05 Boehringer et al 04

21. Current Issues4) fixing the radial density profile • For steady state, E(r) must match jX(r) • Why do clusters have similar jx profiles? • Effervescent heating? (Roychowdhury et al 05) • Damped sound waves? (Fabian et al 04, Ruszkowski et al 05) • Other physics? (Vernaleo & Reynolds 06)

22. Omma & Binney 04 • A more powerful jet disrupts further out • A more concentrated profile disrupts jet further in • Later jet ignition → bigger outburst • Later ignition → more centrally concentrated density profile • So later ignition ! strong, centrally concentrated heating

23. Simulations • Start from present configuration of Hydra (David et al 2000) • Wait (i) 262 Myr (ii) 300 Myr • In (ii) extra 4x1059 erg lost to radiation, so add 8x1059 erg rather than 4x1059 erg as in (i) • EBondi=5(M/109M¯)2£1059erg in 262Myr; EBondi=7(M/109M¯)2£1059erg in 300Myr

24. Outbursts have undone 300 Myr of cooling • System with later ignition ends less centrally concentrated • Implies that systems can oscillate around an attracting profile

25. Current Issues5) Shocks • Unsharp-masked X-ray images show ripples (Fabian et al 03, 06; Forman et al 03) • Are these sound waves / weak shocks? • Expected T variations not seen (Fabian et al 06) • Or Gravity waves?

26. Conclusions • “Cooling flows” thermostated by AGN • This was predicted in early 90s • AGN are in “radio mode” and have high mechanical efficiency • They heat episodically via jets (non-adiabatic) • Central gas density regulates energy production • Profile of heat generation regulated by density profile of gas via radius of jet disruption • Nature of small-scale structures still unclear

27. Part II: Connection to Galaxy Formation (Binney 04; Dekel 04)

28. CDM Clustering • Small-scale cosmic web of DM develops around z~30 • Subsequently larger-scale webs form from collapsed structures from earlier webs • Gradually accumulate superposition of halos with ~power-law mass function • Mass function unlike galaxy L function

29. Galaxy Formation • Low M galaxies suppressed by photoionization, evaporation & SN feedback (Efstathiou 92; Dekel & Silk 86; Dekel 04) • Infalling gas shocks • Accretion shock near centre if tcool<tfree-fall • Condition holds for most mass in halos with M<1012M¯ (Dekel & Birnboim 03, 06)

30. Lumpy Accretion • Extended Press-Schechter predicts lumpy accretion (mergers/cannibalism) • Accretion shock unhelpful concept for lumpy accretion • So without SN heating all gas cold

31. SN Heating • After starbursts SN heat much gas to ~107K • Flows out of halos with vc<100 km s-1 (Larson 74, Dekel & Silk 86) • In larger halos SN-heated gas accumulates • As infall continues, central density rises • Cannot be stabilized by SN heating

32. AGN Heating • tcool=3/2mpkT/n shortest @ centre • BH accretion rate rises with n0 • Mechanical L stabilizes hot gas • In absence of cold infall hot gas cannot cool

33. Cold Infall • Cold infall widely observed: • Magellanic stream • Perseus filaments • At hot/cold interface • (a) ablation by conduction/mixing (small blobs) • (b) condensation and star formation (larger blobs) • Conduction more important at high T (Nipoti & B 04) Conselice et al 01

34. Connection with BH growth • BH growth known to take place in bursts: • Yu & Tremaine (2002) find (i) AGN have radiated in optical/UV as much E as released by all nuclear BHs; (ii) L~LEdd and ε>0.1 needed to produce observed quasars from observed BHs • @LEdd M~exp(t/tSalpeter); tSalpeter~25 Myr • So M from 103M¯ To 109M¯ with 14tS~0.4Gyr and 10Gyr at <0.05LEdd • Magorrian relation M~Mbulge, high α/Fe of bulges, high ages of bulges all imply LEdd (quasar) phase associated rapid star formation • Conjecture this is when there is cold gas @ centre • Episodes end when well deep enough to trap 107K gas; then Mdot 0.002 to 0.02 M¯/yr to offset 1043 – 1044 erg/s of LX

35. Semianalytic GF(Croton et al 06 & Cattaneo et al 06) • From model of DM clustering take merger history of halo population • Fraction 0.17 or 0.14 of M in baryons • Primary halos have hot gas, cold gas, stars • Secondary halos has stars & cold gas • They spiral in by dynamical friction • Bulges form in (a) merger-driven starbursts and (b) disk instabilities • SNe expel gas

36. Cattaneo et al (06) • Standard models: • Gas shock heated & arranged in singular isothermal sphere • Cools to exponential disk • dot M*=Mcool/(tdyn) • ½ dot Mwindve2=SNsnESNdot M* • Makes too many bright blue galaxies • Makes luminous galaxies too late • Lack of COMBO-17 red galaxies

37. New Models • Sharp transition: cold infall ! virialization @ Mcrit=Mshock£ Min(1,101.3(z-zc) • At M>Mcrit reheat cold gas • Now dot M*=(1+z) Mcold/(tdyn) • Find '0.6, Mshock'2£1012M¯, zc'3.2

38. New Models • Good agreement global SFR

39. Croton et al (06) • Gas shock heated to Tvir & cools to disk • Either immediately (rcool>rvir) or at rate 4(rcool)rcool2 drcool/dt • In disk steady SF at rate / (m-mcrit)/tdyn • SN inject energy ESN/m* to mass 3.5m* • When in hot halo gas has energy 3.5£0.5m*Vc2 • Surplus E used to eject gas from halo

40. AGN Feedback • Croton et al follow mBH(t) • Mergers drive quasar mode: mBH=f mcold/[1+(280/Vvir)2] with f(msat/mhost) • No feedback • In radio mode dmBH/dt/ mBHfhotVvir3 • LBH= c2(dmBH/dt) offsets radiative cooling

41. Croton et al Results • Feedback suppresses cooling at large Vvir and low z • Eliminates very luminous galaxies • Establishes red/blue dichotomy Croton et al Croton et al

42. Conclusions • Now clear that AGN heating important for GF • Distinguish quasar & RG modes • RG mode when dense atmosphere @ Tvir • RG mode only in massive halos • BHs grow principally from cold gas simultaneously with rapid SF in bulge • Gas at Tvir never forms stars – galaxies don’t form from cooling gas • Gravitational heating certainly unimportant at M<2£1012M¯ • SN heating vital • Role of thermal conductivity/ablation to be clarified

43. Heating CFs by BHs • In absence of heating n(0)→∞ in t<tcool(0) • Such a cooling catastrophe must provoke a response from the central BH

44. Bondi accretion • Area of sonic flow • Particle density • Accretion rate • Luminosity • So balance possible with E α ∫ dt LX

45. Characteristic M*=3x1010M. (Kauffmann et al 03) • At M>M* dSB/dM=0; at M<M* dSB/dM>0 • At M>M* galaxies old; at M<M* younger • At M>M* light centrally concentrated

46. Theory of Galaxy Formation • Standard picture: gas heated to Tvir on falling into Φ(Rees & Ostriker 1977; White & Rees 1978) • Actually fraction f enters at T<<Tvir(Binney 1977; Katz et al 2003; Birnboim & Dekel 2003) • f~1 on galaxy scales M* and below Katz et al 02 Birnboim & Dekel 04