Transcript Growth of SMBH - Pennsylvania State University

Growth of SMBH studied
through X-ray surveys
H. M. L. G. Flohic
Motivation
• Local galaxies all harbor SMBH (from
stellar and gas dynamics) whether
quiescent or active
• Mass of SMBH related to properties of host
galaxy (Lbul, σ*)  coeval evolution of BH
and host galaxy
• To understand learn more about galaxy
formation and evolution, it is important to
determine how SMBH grow
How do SMBH grow?
• 2 possibilities:
– Accretion of material from host galaxy (AGN)
– Merger (colliding galaxies)
• Which one is the most important on long
timescales?
How can we tell?
• Assume all SMBH growth through accretion
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(AGN).
Observe AGNs at a high redshift and deduce
their mass and mass accretion rate from their
intrinsic luminosity
Integrate mass accretion rate over time for the
whole population and extrapolate the mass the
SMBH would have at z=0 (relic AGN)
Compare with masses of SMBH observed in local
galaxies (local BHs)
If they match, assumption was correct otherwise
mergers are important too.
Challenges in this method
• Don’t miss any AGN!
– Beware of obscuration
– Beware of selection effects (from limited band width)
• Need intrinsic luminosity of AGN:
– Beware of contamination from host galaxy
– Make correct bolometric correction
• Relation between mass accretion rate and
intrinsic luminosity has fudge factors
• Scatter in relation between SMBH mass and host
galaxy properties could introduce error in local
result
 Be careful and make consistency checks along
the way
AGN populations
• Use a complete survey of AGNs at a high
redshift (e.g. z ~3 => 85% of age
universe) (Marconi et al. 2004)
• Use the X-ray background (XRB) =
integrated X-ray emission from AGN
(starburst galaxies contribution negligible)
(Fabian 2004)
Step 1: Local BH mass function
• Local BH mass
function can be
determined from Lbul
or σ* function.
• Both relations have
some scatter that can
modify the results:
• Need to use a complete
sample covering the whole
morphology range:
• Note that
– the results are consistent for
different surveys.
– late type galaxies contribute
to the low-mass end of the
mass function
– ρ(BH) = 4.6 x 105 MO Mpc-3
Step 2: AGN relics mass function
• BH mass function of AGNs has a time
dependence  continuity equation
• Some assumptions and some algebra:
which can easily be integrated over M:
Assumptions:
• SMBH grows only through accretion at a
fraction λ of LEdd and converts mass to
energy with efficiency Є
• Neglect creation of BH and mergers
• λ and Є are constant
• Energy either radiated (Є) or lost inside
the BH horizon (no jets)
• We follow the evolution of all the BH that
active at the starting redshift.
Easier way to get the same result:
Erad=ЄMc2
• Divide by volume:
Urad= ЄρBHc2=UT(1- Є)
• So what bother with the more
complicated way?
– Intermediate results: BH mass function,
accreting fraction, time evolution
– Constraints on λ and Є
– Good for the soul
All you need is…
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… the complete intrinsic luminosity function at a
given redshift.
Marconi tried 3 surveys (all have selection
effects):
– Boyle - quasars selected from blue colors
– Miyaji - soft X-ray selected AGNs
– Ueda - hard X-ray selected AGNs
• Survey in a given bandpass  need bolometric
correction
Bolometric correction
• Construct a sample template:
– UV – optical : broken power law
– Big blue bump  α =2
(Rayleigh–Jeans tail)
– Power law + reflection
component in the X-ray (>1
keV)
– Exponential cutoff at 500 keV
– Rescaled so that
From LF to relic MF
– λ = 1, Є = 0.1, δ = 1,
zs=3
– MF at z=3 2 order of
magnitude below z=0 
most growth after z=3
– Most massive SMBH
grew during quasar
phase
Varying the initial conditions:
• Є is simple scaling factor
• λ has complex effect on
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BHMF
Varying δ has no effect
Varying zs has no effect
on BMHF  growth
happens at a small
redshift
Compare local BHMF and relic:
• No discrepancies in the
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mass distribution
Ueda is the most
complete survey
ρUeda= 2.2 x 105 MO Mpc-3
ρlocal= 4.6 x 105 MO Mpc-3
Relic BHMF slightly under
the local one  did not
account for obscured
AGNs
Missing AGN population
• Ueda does not detect
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Compton thick
sources (log NH >24)
 need to correct
BHMF for that
Assume the number
of galaxies in the 2324 bin equals that in
the 24-25 and 25 -**
bins
So need to multiply
BHMF by a factor of
1.6
New and improved BHMF
•ρUeda=3.5x 105 MO Mpc-3
•ρlocal= 4.6x 105 MO Mpc-3
– Good agreement
our starting
assumption was
correct – mergers
are negligeable
– λ = 1, Є = 0.1, δ =
1, zs=3
– We could vary λ
and Є
Cherry on top
• Using the same obscuration, one can
reproduce the XRB spectrum
Best fit
• Є = 0.08, λ = 0.5
• Є appears above Є for
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a non-rotating black
hole  on average,
SMBH are rotating
(note that mergers spin
BH down)
0.1 < λ < 1.7 so BH
grow mostly during
luminous phases
(comparable to
observed values of
SDSS quasars)
Growth history
– Lower mass SMBH grow at a later time than more
massive one  anti-hierarchical growth of SMBH
– All SMBH gain at least 95% of their mass after
redshift 3
Coeval evolution with host galaxy
• Cosmic accretion
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history has same
redshift dependence
has cosmic SFR
history
Can explain the MBHLbul and MBH-σ*
relations
Lifetime of AGNs
– Higher mass SMBH turn off at a higher redshift
– Lower mass BH have longer lifetime
 Consistent with the anti-hierarchical growth
Conclusion from Marconi:
• Growth of SMBH done mostly through
accretion (not mergers)
• Anti-hierarchical growth (high mass first)
• Most growth done at z<3
• Most growth in luminous AGN phase
• No high efficiency required (slightly
rotating BH)
Using the XRB
• Remember ρBH=UT(1- Є)/ Єc2
• Then ρBH=Uobs(1- Є)(1+<z>)/ Єc2
• Uobs can be estimated from the XRB
• Key point is <z>
How it was done (Fabian & Iwasawa)
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Assume <z>=2, Є=0.1
ρXRB=6x105 MO Mpc-3
ρlocal=4.6x105 MO Mpc-3
Relic BHMF too high so
– need a greater Є  BH are
rotating fast
– mergers are not negligible
• Both are incompatible since
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mergers spin down BH
High Є does not allow BH to
grow from small seeds
What has changed
• Obscured sources peak
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at a lower redshift than
obscured sources
<z> is then lower than
previously assumed
Using <z>=1.1 &
Є=0.1, ρXRB=4.2x105
MO Mpc-3
No need for high spin
BH
Mergers are negligible
Another cherry
Obscured AGNs have the redshift distribution as star-forming
galaxies
 starburst could feed and obscure the AGN
Why not quasars?
• Quasars have much higher luminosity
• Radiation pressure could blow away the
gas, impairing star formation and stopping
the feeding
 Feedback from the AGN explaining the
MBH-Lbul and MBH-σ* relations
Can we prove the role of obscuration?
• X-ray absorbed and re-emitted in IR, then
redshifted to sub-mm
Contribute to the IRB & sub-mm galaxies
should host AGN
• Observed a 3-4% contribution of AGN to
whole IRB but data not good enough to
rule out (need results from Spitzer)
• In CDF-N, 5/10 SCUBA sources host AGN
but only small contributor to bolometric
luminosity (dominated starburst)
Conclusions
• Comparison of mass density/function of local
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SMBH and AGNs at high z (from survey or XRB)
gives information on growth of SMBH
Growth done mostly though accretion (not
mergers) in luminous AGN phase
Anti-hierarchical growth (most massive built 1st
and in quasar phase)
As time goes, growing SMBH become
increasingly obscured (peaking at a redshift
different from quasars)
Growth correlated with star formation in host
galaxy
Tada!