1. Growth of SMBH studied through X-ray surveys
H. M. L. G. Flohic

2. 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

3. 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?

4. How can we tell? Assume all SMBH growth through accretion (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.

5. 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

6. 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)

7. 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:

8. 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

9. 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:

10. 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.

11. 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

12. All you need is…
… 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

13. 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

14. 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

15. Varying the initial conditions:
Є is simple scaling factor
λ has complex effect on BHMF
Varying δ has no effect
Varying zs has no effect on BMHF  growth happens at a small redshift

16. Compare local BHMF and relic:
No discrepancies in the 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

17. Missing AGN population
Ueda does not detect Compton thick sources (log NH >24)  need to correct BHMF for that
Assume the number of galaxies in the bin equals that in the and 25 -** bins
So need to multiply BHMF by a factor of 1.6

18. 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

19. Cherry on top
Using the same obscuration, one can reproduce the XRB spectrum

20. Best fit
Є = 0.08, λ = 0.5
Є appears above Є for 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)

21. 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

22. Coeval evolution with host galaxy
Cosmic accretion history has same redshift dependence has cosmic SFR history
Can explain the MBH-Lbul and MBH-σ* relations

23. Lifetime of AGNs Higher mass SMBH turn off at a higher redshift
Lower mass BH have longer lifetime
 Consistent with the anti-hierarchical growth

24. 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)

25. 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>

26. How it was done (Fabian & Iwasawa)
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 mergers spin down BH
High Є does not allow BH to grow from small seeds

27. What has changed
Obscured sources peak 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

28. Another cherry
Obscured AGNs have the redshift distribution as star-forming galaxies
 starburst could feed and obscure the AGN

29. 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

30. 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)

31. Conclusions
Comparison of mass density/function of local 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

32. Tada!