Transcript Cooling flows and Galaxy formation

Cooling flows and Galaxy
formation
James Binney
Oxford University
Outline
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Phenomenology of CFs
Physics of heating
Standard galaxy formation
Galaxy formation revisted
collaborators
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Len Cowie
Gavin Tabor
Henrik Omma
Fathallah Alouani Bibi
Carlo Nipoti
Filippo Fraternali
The phenomenon
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Thermal X-rays from
Clusters of galaxies
Groups of galaxies
Individual galaxies
Jetha + 07
Perseus (Fabian + 03)
Cooling times
short
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Jetha + 07
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Usually T(0) < T(1) by factor ~ 3
In absence of heating
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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)
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@ centre expect cooling catastrophe
Boehringer + 02
Central accumulation?
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Is cold gas streaming into centre?
In general no because:
Absence of young stars, of whatever mass
1.44-2 keV
(Prestwich
et al 97)
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X-ray SB profile insufficiently peaked
X-ray spectrum shows little gas at
T<1/3 T1 (Boehringer + 02, Peterson + 03)
Peterson + 03
@ the centre of Perseus
Salome + 06
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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
Heating
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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
Evidence for mechanical heating
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First cavity seen in 1993 (Boehringer et al)
Chandra sees many cavities (1999--)
Cavities often coincide with non-thermal
radio emission
In M87
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Chandra resolves rBondi
(Di Matteo et al 03)
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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)
Simulations
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Adaptive grid 3d hydro simulations
Extended heat injection !
Omma thesis
05
realistic entropy
profiles
(Omma & Binney 05)
Stress irreversibility of cavity creation
(Binney et al 07)
Donahue + 05
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
Summary
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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
Galaxy formation
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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
Tvir
T!
White & Rees (1978) ff
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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
Suppression of SF
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On smallest scales:
photoionization, evaporation
(Efstathiou 92; Dekel 04)
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On larger scales:
SN feedback (Dekel & Silk 86)
GD II
Trapped gas (Binney 2004)
M/L=220
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With standard IMF, SNe yield
~keV/particle ! TSN~107K
If Tvir<TSN heated gas flows out
Baldry + 04
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
GF by cooling?
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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?
Cold infall
(Binney 2004)
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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)
Role of AGN
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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
Onset of sterility
Peek + 07
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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
Stopping Replenishment
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Atmosphere of trapped gas at Tvir affects
replenishment in 2 ways:
1. Drag on infalling clouds
2. Evaporation of cold gas
Drag
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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
NGC 5746
(Rasmussen + 07)
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Key transition object; vc=310 km s-1
Spherical halo unconnected to SFing disk
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 + 05
(Fraternali + B 07)
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Nipoti + B 07
Cored & Power-law
Es
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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
Nipoti & B 07
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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
Summary
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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
Summary (2)
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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
Summary (3)
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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