The Xray background in the Chandra and XMMNewton era

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The X-ray background in the Chandra and
XMM-Newton era
Andrea Comastri (INAF-OABologna-Italy) Robert
o Gilli (INAF-OABologna-Italy) Guenthe
r Hasinger (MPE-Garching-Germany) Alessandro
Marconi (INAF-OAArcetri-Italy)
Gilli, Comastri, Hasinger 2006 submitted to
AA Marconi, Gilli, Comastri in preparation
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• Deep X-ray surveys have resolved some 80 of the
  XRB (below a few keV ) but only 50 gt 6 keV
  and a few above 10 keV.
• Wealth of X-ray and multiwavelength follow-up
  available unlikely to be substantially modified
  in the next decade or so
• Worth to make an effort to constrain the missing
  population (Compton Thick AGN) and make solid
  prediction for future missions
• The missing population may provide an important
  contribution to the BH mass function SMBH/galaxy
  evolution, accretion rates, Eddington ratios,
• Provide robust predictions to be compared with
  the currently ongoing efforts to efficiently
  select obscured AGN

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Model scheme

• XRB flux uncertain, so use the more robust
  constraints below 10 keV (eg. source counts) to
  lock the properties (eg obs/unobs ratio, NH
  dist.) of the Compton Thin (log NH lt 24) AGN
• Estimate the Compton Thin/Unobs. Ratio by
  comparing hard vs. soft XLF.
• Absorption distribution from X-ray counts.
• Include continuum slope dispersion.
• Add Compton thick AGN to fit the 30 keV bump
• Verify assumptions/make predictions on Compton
  Thick AGN

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Unabsorbed logNHlt21 (plus Compton reflection)
Compton-Thin 21ltlogNHlt24 Compton-Thick logNHgt2
4 Mildly (log NH 24-25) (NGC 6240,
Circinus) Heavily (log NH gt25) (NGC1068)
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Hard XLF Compton Thin unobscured (Ueda
03) Soft XLF unobscured (Hasinger05)
RS thin/unobs. _at_ logLX lt 43 RQ thin/unobs. _at_
logLX gt 45
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Hard XLF La Franca05
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Best fit ratios 4 at low Log Lx lt
44 Luminosities 1 at high Log Lx gt
44 luminosities
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Obscured AGN fraction vs luminosity
Observed Intrinsic (i.e.
folded with selection effects)
Akylas06
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X-ray logN-logS
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NH distribution
Thick
T h i n
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Obscured AGN fraction vs sample limiting flux
All abs.
All abs.
Thick
Thick
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• Correction for Compton-Thick sources from XRB
  models ? whole
• AGN pop considered
• The only free parameters are the accretion
  efficiency and Eddington ratio
• L e dM/dt c2
• L ? LEdd

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• Determine locus in e-? plane where there is the
  best match between local and relic BHMF!
• e0.04-0.10 ?0.08-0.5 which are consistent
  with common beliefs on AGNs

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Summary

• The comparison between the soft and hard XLF
  indicates that the obscured/unobscured ratio
  decreases with increasing Lx No evidence of
  redshift dependence.
• The NH distribution increases towards high NH
• Large population of Compton-thick AGN (as
  many
• as Compton-thin, equally splitted between
  mildly and heavily). Some of the mildly CT have
  been detected in deep X-ray surveys see also
  deep IR searches
• Heavily ? The XRB model gives a suggestion
  
• BH mass density argument will help CT
  space density degenerates with accretion
  efficiency and geometry of reflecting thick
  matter
• To be explored CT XLF - NHf(L,z) - IR
  background