Growth of SMBH studied through X-ray surveys

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Growth of SMBH studied through X-ray surveys

• H. M. L. G. Flohic

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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, s) ? coeval evolution of BH and host
  galaxy
• To understand learn more about galaxy formation
  and evolution, it is important to determine how
  SMBH grow

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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?

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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 z0 (relic AGN)
• Compare with masses of SMBH observed in local
  galaxies (local BHs)
• If they match, assumption was correct otherwise
  mergers are important too.

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Challenges in this method

• Dont 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

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AGN populations

• Use a complete survey of AGNs at a high redshift
  (e.g. z 3 gt 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)

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Step 1 Local BH mass function

• Local BH mass function can be determined from
  Lbul or s function.
• Both relations have some scatter that can modify
  the results

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• 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
• ?(BH) 4.6 x 105 MO Mpc-3

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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

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Assumptions

• SMBH grows only through accretion at a fraction ?
  of LEdd and converts mass to energy with
  efficiency ?
• Neglect creation of BH and mergers
• ? and ? are constant
• Energy either radiated (?) or lost inside the BH
  horizon (no jets)
• We follow the evolution of all the BH that active
  at the starting redshift.

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Easier way to get the same result

• Erad?Mc2
• Divide by volume
• Urad ??BHc2UT(1- ?)
• So what bother with the more complicated way?
• Intermediate results BH mass function, accreting
  fraction, time evolution
• Constraints on ? and ?
• Good for the soul

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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

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Bolometric correction

• Construct a sample template
• UV optical broken power law
• Big blue bump ? a 2 (RayleighJeans tail)
• Power law reflection component in the X-ray (gt1
  keV)
• Exponential cutoff at 500 keV
• Rescaled so that

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From LF to relic MF

• ? 1, ? 0.1, d 1, zs3
• MF at z3 2 order of magnitude below z0 ? most
  growth after z3
• Most massive SMBH grew during quasar phase

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Varying the initial conditions

• ? is simple scaling factor
• ? has complex effect on BHMF
• Varying d has no effect
• Varying zs has no effect on BMHF ? growth happens
  at a small redshift

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Compare local BHMF and relic

• No discrepancies in the mass distribution
• Ueda is the most complete survey
• ?Ueda 2.2 x 105 MO Mpc-3
• ?local 4.6 x 105 MO Mpc-3
• Relic BHMF slightly under the local one ? did not
  account for obscured AGNs

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Missing AGN population

• Ueda does not detect Compton thick sources (log
  NH gt24) ? need to correct BHMF for that
• Assume the number of galaxies in the 23-24 bin
  equals that in the 24-25 and 25 - bins
• So need to multiply BHMF by a factor of 1.6

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New and improved BHMF

• ?Ueda3.5x 105 MO Mpc-3
• ?local 4.6x 105 MO Mpc-3
• Good agreement ?our starting assumption was
  correct mergers are negligeable
• ? 1, ? 0.1, d 1, zs3
• We could vary ? and ?

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Cherry on top

• Using the same obscuration, one can reproduce the
  XRB spectrum

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Best fit

• ? 0.08, ? 0.5
• ? appears above ? for a non-rotating black hole ?
  on average, SMBH are rotating (note that mergers
  spin BH down)
• 0.1 lt ? lt 1.7 so BH grow mostly during luminous
  phases (comparable to observed values of SDSS
  quasars)

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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

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Coeval evolution with host galaxy

• Cosmic accretion history has same redshift
  dependence has cosmic SFR history
• Can explain the MBH-Lbul and MBH-s relations

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Lifetime of AGNs

• Higher mass SMBH turn off at a higher redshift
• Lower mass BH have longer lifetime
• ? Consistent with the anti-hierarchical growth

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Conclusion from Marconi

• Growth of SMBH done mostly through accretion (not
  mergers)
• Anti-hierarchical growth (high mass first)
• Most growth done at zlt3
• Most growth in luminous AGN phase
• No high efficiency required (slightly rotating BH)

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Using the XRB

• Remember ?BHUT(1- ?)/ ?c2
• Then ?BHUobs(1- ?)(1ltzgt)/ ?c2
• Uobs can be estimated from the XRB
• Key point is ltzgt

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How it was done (Fabian Iwasawa)

• Assume ltzgt2, ?0.1
• ?XRB6x105 MO Mpc-3
• ?local4.6x105 MO Mpc-3
• Relic BHMF too high so
• need a greater ? ? BH are rotating fast
• mergers are not negligible
• Both are incompatible since mergers spin down BH
• High ? does not allow BH to grow from small seeds

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What has changed

• Obscured sources peak at a lower redshift than
  obscured sources
• ltzgt is then lower than previously assumed
• Using ltzgt1.1 ?0.1, ?XRB4.2x105 MO Mpc-3
• No need for high spin BH
• Mergers are negligible

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Another cherry
Obscured AGNs have the redshift distribution as
star-forming galaxies ? starburst could feed and
obscure the AGN
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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-s relations

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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)

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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

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Tada!