Transcript Cooling Flows & Galaxy Formation

Cooling Flows & Galaxy
Formation
James Binney
Oxford University
Outline
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Cooling flows – historical introduction
Current issues in CF dynamics
Much work from Henrik Omma’s (05) thesis
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SEQUEL TOMORROW
Implications for galaxy formation and BH growth
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“Cooling flows”
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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
Distributed mass drop-out
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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
G modes
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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!
AGN Heating
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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
1993 - 2001
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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)
2001 – Chandra & XMM-Newton
XMM doesn’t see lines of <106K gas
 (Bohringer
XMM shows
that deficit of photons at
et al 02)
<1keV not due to internal absorption
 But associated with “floor” T' Tvir/3
 Chandra shows that radio plasma has
displaced thermal plasma
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(Peterson et al 02)
Bubble Models
(Churazov et al 2001; Quilis et al 2001; Brueggen & Kaiser
2001,2002; Brueggen et al 2002)
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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
Injection Models
(Quillis et al 01, Brueggen & Kaiser 02)
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Add thermal energy at some fixed offcentre location
Poor representation of effects of moving
jet hot-spot
Brueggen & Kaiser 02
Jet Simulations
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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
Omma’s Simulations
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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
Outward increasing entropy
Omma thesis 05
Donahue 04
Current Issues
1) enough E?
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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)
In M87
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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)
Current Issues
2) the duty cycle
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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
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Define cavities by
<0/4
Evaluate PV
Peaks at only 10% of
actual input
Omma 05
Current Issues
3) does mixing destroy Z gradients?
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Follow tracer dye from (a) r<5kpc, and
(b) 5<r<77 kpc
Omma 05
Effect on Z gradient
Omma thesis 05
Boehringer et al 04
Current Issues
4) fixing the radial density profile
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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)
Omma & Binney 04
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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
Simulations
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Start from present configuration of Hydra
(David et al 2000)
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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
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Outbursts have undone 300 Myr of cooling
System with later ignition ends less centrally
concentrated
Implies that systems can oscillate around an
attracting profile
Current Issues
5) Shocks
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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?
Conclusions
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“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
Part II:
Connection to
Galaxy Formation
(Binney 04; Dekel 04)
CDM Clustering
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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
Galaxy Formation
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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)
Lumpy Accretion
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Extended Press-Schechter predicts lumpy
accretion (mergers/cannibalism)
Accretion shock unhelpful concept for
lumpy accretion
So without SN heating all gas cold
SN Heating
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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
AGN Heating
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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
Cold Infall
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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)
Conselice et al 01
Conduction more important at high T
(Nipoti & B 04)
Connection with BH growth
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BH growth known to take place in bursts:
Yu & Tremaine (2002) find
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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
Semianalytic GF
(Croton et al 06 & Cattaneo et al 06)
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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
Cattaneo et al (06)
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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
New Models
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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
New Models
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Good agreement global SFR
Croton et al (06)
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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
AGN Feedback
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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
Croton et al Results
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Feedback suppresses cooling at large Vvir
and low z
Eliminates very luminous galaxies
Establishes red/blue dichotomy
Croton et al
Croton et al
Conclusions
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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
Heating CFs by BHs
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In absence of heating n(0)→∞ in
t<tcool(0)
Such a cooling catastrophe must provoke
a response from the central BH
Bondi accretion
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Area of sonic flow
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Particle density
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Accretion rate
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Luminosity
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So balance possible with E α ∫ dt LX
Characteristic M*=3x1010M.
(Kauffmann et al 03)
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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
Theory of Galaxy Formation
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Standard picture: gas heated to Tvir on
falling into Φ
(Rees & Ostriker 1977; White & Rees 1978)
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Actually fraction f enters at T<<Tvir
(Binney 1977; Katz et al 2003; Birnboim & Dekel 2003)
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f~1 on galaxy scales M* and below
Katz et al 02
Birnboim & Dekel 04