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Cooling flows and Galaxy formation

Cooling flows and Galaxy formation. James Binney Oxford University. Outline. Phenomenology of CFs Physics of heating Standard galaxy formation Galaxy formation revisted. collaborators. Len Cowie Gavin Tabor Henrik Omma Fathallah Alouani Bibi Carlo Nipoti Filippo Fraternali.

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Cooling flows and Galaxy formation

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  1. Cooling flows and Galaxy formation James Binney Oxford University

  2. Outline • Phenomenology of CFs • Physics of heating • Standard galaxy formation • Galaxy formation revisted

  3. collaborators • Len Cowie • Gavin Tabor • Henrik Omma • Fathallah Alouani Bibi • Carlo Nipoti • Filippo Fraternali

  4. The phenomenon Jetha + 07 • Thermal X-rays from • Clusters of galaxies • Groups of galaxies • Individual galaxies Perseus (Fabian + 03)

  5. Cooling times • short • Usually T(0) < T(1) by factor ~ 3 Jetha + 07

  6. In absence of heating • Field (1965): Cooling causes runaway growth of T differences • T will drop fastest where entropy is lowest • Malagoli et al (1987): This will be @ centre because away from centre cool (overdense) regions will sink till they reach gas with the same specific entropy (cf Maller & Bullock 04) • @ centre expect cooling catastrophe

  7. Boehringer + 02 Central accumulation? • Is cold gas streaming into centre? • In general no because: • Absence of young stars, of whatever mass (Prestwich et al 97) • X-ray SB profile insufficiently peaked • X-ray spectrum shows little gas at T<1/3 T1(Boehringer + 02, Peterson + 03) 1.44-2 keV Peterson + 03

  8. @ the centre of Perseus Salome + 06 • Molecular gas detected • By J=0,1,2.. Transitions of CO (Edge + 01, Salome + 06) • By rotation-vibration transitions of H2 (Hatch + 05) • Atomic gas detected in H etc • Gas extends out in filaments • Soft X-ray emission from around filaments (Fabian + 03) • Not rotating • Less gas (~4£1010M¯) than expected if catastrophic cooling for Gyrs

  9. Heating • Invariably a massive elliptical @ centre • Such objects host central BHs • And central non-thermal radio sources • The Bondi accretion rate onto BH is temperature-dependent • So accretion rate rises steeply with falling T

  10. Evidence for mechanical heating • First cavity seen in 1993 (Boehringer et al) • Chandra sees many cavities (1999--) • Cavities often coincide with non-thermal radio emission

  11. In M87 • Chandra resolves rBondi • (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 fraction MBondi & heating on kpc scales with high efficiency (Binney & Tabor 95)

  12. Simulations • Adaptive grid 3d hydro simulations • Extended heat injection ! • realistic entropy profiles (Omma & Binney 05) • Stress irreversibility of cavity creation (Binney et al 07) • Explain how heating statistically matched to cooling (Omma & Binney 05) • Vjet= 10,000 km/s Entr2kpc.mov • Vjet=20,000 km/s \u\henrik\20kv\entr.mov Omma thesis 05 Donahue + 05

  13. Summary • Deep potential wells filled with gas at Tvir • Gas doesn’t cool: thermostated by AGN • Probably regulated by Bondi accretion of gas at Tvir • Heating mechanical • Bubbles dynamical & only tips of icebergs

  14. Galaxy formation • Dark matter clusters from z'3000 • Baryons cluster with DM from z'1000 • At z~20 small regions start collapsing • On collapse gas shocked • In absence of cooling T! Tvir

  15. White & Rees (1978) ff • CDM spectrum has much power on small scales • So large fraction of baryons quickly collapse into small-scale halos • CDM halos are cuspy, so survive on falling in to much larger halos • So expect bulk of baryons to be in myriads of small galaxies • In reality ~1/4 of baryons in galaxies, and most in L*' 1012M¯ halos • Conclude: star formation suppressed in small halos

  16. Suppression of SF • On smallest scales: photoionization, evaporation (Efstathiou 92; Dekel 04) • On larger scales: SN feedback (Dekel & Silk 86)

  17. GD II Trapped gas (Binney 2004) M/L=220 • With standard IMF, SNe yield ~keV/particle ! TSN~107K • If Tvir<TSN heated gas flows out • Once Tvir>TSN it accumulates • In classic semi-analytic models of GF ! “overcooling” and formation of many luminous blue galaxies (Benson et al 03) • Actually most luminous galaxies belong to red sequence: no recent SF Baldry + 04

  18. GF by cooling? • Galaxies of red sequence either have gas trapped @ Tvir (X-rays) or are subhalos of halos with gas @ Tvir • White & Rees (78), White & Frenk (91) assumed gas shock-heated to Tvir on infall & GF occurred on cooling • But CF data show trapped gas doesn’t cool! • So how do galaxies form?

  19. Cold infall (Binney 2004) • In simulations, higher resolution ! higher density ! faster cooling • Dekel & Birnboim (03, 06) argued gas only heated when M>1012M¯ • Corroborates results from clustering simulations (Keres + 05) • So blue-cloud galaxies can form from cold gas • Inefficiently because TSN>Tvir so M(eject)~M(SF)

  20. Role of AGN • Does AGN blast ISM away during a merger? • Easiest at low M • So if ever possible, all galaxies would be red • AGN thermostats trapped gas to Tvir

  21. Onset of sterility Peek + 07 • Star-forming galaxies consume gas in less than tHubble • E.g. MW: 2M¯yr-1 of SF consumes 4£109M¯ in 2 Gyr • Galaxies rejuvenated by infall of cold gas (NGC 4550) • Gas continuously replenished (HVCs; gas from Sgr dwarf, Magellanic Clouds etc) Putman + 03

  22. Stopping Replenishment • Atmosphere of trapped gas at Tvir affects replenishment in 2 ways: • 1. Drag on infalling clouds • 2. Evaporation of cold gas

  23. Drag • mcdv/dt=-Ach v2! v(t)=v0/(1+t/) =v0mc/Ach • With Rc<100 pc, v0=100 km s-1 and nh=10-3cm-3, '300 Myr • So clouds can’t move fast through halo

  24. NGC 5746(Rasmussen + 07) • Key transition object; vc=310 km s-1 • Spherical halo unconnected to SFing disk

  25. Extraplanar HI • SF cycles gas through halo (HVCs; NGC 891; Fraternali & B 06) • Extraplanar HI still rapidly rotating • Not consistent with existence of n=10-3cm-3 non-rotating halo (Fraternali + B 07) Fraternali + 05

  26. Cored & Power-law Es Nipoti + B 07 • Dichotomy in Es: (Faber + 1997, Ferrarese + 06) • Central SB slope <0.3 (CGs) or >0.5 (PLGs) • PLGs: disky, MV>-20.5, large (v/)*, low LX/LB • PLGs younger centres • What’s the connection between X-ray gas and stellar distribution? Ferrarese + 06

  27. Nipoti & B 07 • N-bodies consistent with conjecture: when galaxies with BHs merge, remnant has core with Mdef' MBH by upscattering (Milosavljevic & Merritt) • Will be filled in by SF only if tevap>tdyn • tevap/tdyn smaller by 103 in X-ray luminous CG compared to PLG • So in PLG central SF possible after last merger

  28. Summary • Central BHs thermostat trapped gas at Tvir • Contradicts premise of White-Rees theory • Gas falls into low-M halos cold • SF drive outflow when TSN>Tvir • At M~1012M¯ (a) Tvir~TSN and (b) infall gravitationally heated to Tvir • So for M>1012M¯ halos trap SN-heated gas

  29. Summary (2) • Galaxies in blue cloud while cold infall continues • Galaxies transfer to red sequence when either (a) Tvir>TSN or (b) fall in to halo with Tvir>TSN • Because hot atmosphere kills cold infall by (a) drag on clouds (b) evaporation of clouds

  30. Summary (3) • Trapped gas almost non-rotating • So drag prevents infall feeding disk • After merger SF at centre of lower-L E possible • Explains correlation of LX with optical properties

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