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Everything you wanted to know about the X-ray background …

Everything you wanted to know about the X-ray background …. Andrea Comastri (INAF-OABologna-Italy). Gilli R., Comastri A., Hasinger G. 2006 AA in press astro-ph/0610939. OUTLINE.

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Everything you wanted to know about the X-ray background …

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  1. Everything you wanted to knowabout the X-ray background … Andrea Comastri (INAF-OABologna-Italy) Gilli R., Comastri A., Hasinger G. 2006 AA in press astro-ph/0610939

  2. OUTLINE • Demography and evolution of obscured AGN from XRB models -> uncovering the most elusive accreting Black Holes • Does the unified scheme depend from luminosity and redshift ? MISST • Perspectives for future X-ray multi-wavelength surveys and models ANEW X-ray Surveys Cambridge November 6, 2006

  3. Why is still worth fitting the XRB ? • Deep X-ray surveys have resolved some 80% of the XRB (below a few keV ) but “only” 50% > 6 keV (Worsley+05) and a few % above 10 keV. • Wealth of X-ray and multi-wavelength 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 and for currently ongoing multi- efforts to efficiently select `obscured’ AGN (Risaliti+99, Fiore +03,Tozzi+06,Martinez-Sansigre+05, Georgantopoulos+06; …) X-ray Surveys Cambridge November 6, 2006

  4. Assuming the same evolution of “known” AGN and the intensity of the 30 keV XRB peak it is possible to estimate the “size” of the “mildly” (24 < logNH < 25) Compton Thick AGN population • A complete (fair) census of the missing Compton Thick AGN is important for BH mass function, SMBH/galaxy evolution, accretion efficicency, Eddington ratios, … • The BH mass density argument could also be used to constrain the number of heavily (logNH > 25; i.e. NGC 1068 like) Compton thick AGN X-ray Surveys Cambridge November 6, 2006

  5. X-ray Surveys Cambridge November 6, 2006

  6. Frontera+06 submitted X-ray Surveys Cambridge November 6, 2006

  7. 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 < 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

  8. Unabsorbed: logNH<21 Compton-Thin: 21<logNH<24 (Compton reflection high energy cut-off 200 keV) Compton-Thick: Mildly (log NH =24-25) (NGC 6240, Circinus) Heavily (log NH >25) (NGC1068) Dispersion  = 0.2 X-ray Surveys Cambridge November 6, 2006

  9. Hard XLF= Compton Thin + unobscured Ueda+03 La Franca+05 Soft XLF= unobscured (Hasinger+05) La Franca+05 X-ray Surveys Cambridge November 6, 2006

  10. Best fit ratios ~ 4 at low Log Lx < 44 Luminosities ~ 1 at high Log Lx > 44 luminosities X-ray Surveys Cambridge November 6, 2006

  11. Obscured AGN fraction vs luminosity Observed Intrinsic (i.e. folded with selection effects) Akylas+06 X-ray Surveys Cambridge November 6, 2006

  12. X-ray logN-logS X-ray Surveys Cambridge November 6, 2006

  13. Soft counts are measured with good accuracy over a large range of fluxes X-ray Surveys Cambridge November 6, 2006

  14. X-ray Surveys Cambridge November 6, 2006

  15. NH distribution Thick T h i n X-ray Surveys Cambridge November 6, 2006

  16. The fraction of heavily CT depends from the assumed dispersion and reflection efficiency (2%) ! X-ray Surveys Cambridge November 6, 2006

  17. Obscured AGN fraction vs sample limiting flux All abs. All abs. Thick Thick X-ray Surveys Cambridge November 6, 2006

  18. Correction for Compton-Thick sources from XRB models  whole AGN pop considered • The only free parameters are the accretion efficiency and Eddington ratio L = ε dM/dt c2 L = λ LEdd Marconi+04 X-ray Surveys Cambridge November 6, 2006

  19. 2% 0.5% • Determine locus in ε-λ plane where there is the best match between local and relic BHMF! • ε=0.04-0.10 λ=0.08-0.5 which are consistent with common ‘beliefs’ on AGNs 10% X-ray Surveys Cambridge November 6, 2006

  20. Summary of XRB model results • CT as many as thin , fraction depends from scattering efficiency, dispersion in spectral slopes and 30 keV intensity • More obscured AGN at low L -> at QSO luminosities 1 Thin + 1 Thick for each bright unobscured quasar • A “high” 2-10 keV XRB intensity cannot be easily accounted for without violating other constraints (counts, average spectra,…) • Predictions for the space density of obscured (CT) AGN to be compared with present (Spitzer) and future (Herschel) IR surveys and especially > 10 keV survey (Simbol-X) X-ray Surveys Cambridge November 6, 2006

  21. Luminosity and redshift dependence • Obscuration (anti)-correlates with Luminosity (Lawrence & Elvis 1982) -> Ueda+03, Hasinger04, La Franca+05 … but see Dwelly & Page 06 • The obscured fraction increases with z (La Franca+05, Ballantyne+05, Treister & Urry 06) or remains constant (Ueda+03, Hasinger04, Tozzi+06; Dwelly & Page 06; Akylas+06) X-ray Surveys Cambridge November 6, 2006

  22. Need to uniformely sample the Luminosity-Redshift Plane • Take into account selection biases associated to low counting statistic • Incompleteness of spectroscopic redshifts and photo-z uncertainties X-ray Surveys Cambridge November 6, 2006

  23. The Cosmic Cycle of Galaxy and AGN evolution Mergers between gas rich galaxies drive gas which fuel both SF and QSO activity (QSO mode) Obscured growth (ULIRG, SCUBA phase, 4pi Covering ?) BH feedback expels Gas --> BL QSO Shut down of BH activity dead quasars (or slowly accreting BH) in red galaxies (radio mode) The QSO light curves are mass and obscuration dependent (Hopkins et al. 2005) X-ray Surveys Cambridge November 6, 2006

  24. The evolution of both bright and faint end can be better measured with a bolometric approach (modulo Compton Thick) AGN activity • Models predict bolometric luminosity/properties  bolometric approach is needed for a proper census of SMBH (most of them are obscured or elusive) • Bolometric LF and evolution is a key parameter (poorly known–”attempt” by Hopkins+06, HX,SX, B-band and 15 micron, obscuration and SEDs are luminosity dependent and likely redshift dependent) X-ray Surveys Cambridge November 6, 2006

  25. Summary A proper census of SMBH demography and evolution (especially for the most obscured sources) cannot rely only on multi- follow-ups of X-ray surveys but requires a bolometric approach : multiwavelength selection and in particular IR (Spitzer) + XRB and Mass density/function arguments -> “IR background as a bonus” Fit the data (XRB, counts, …) with a time dependent model for the AGN activity to account for Redshift and Luminosity dependence.

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