Risolvere il Background X al suo picco Andrea Comastri (INAF-OABologna) Roberto Gilli (INAF-OABologna) K. Iwasawa (INAF-OABologna) C. Vignali (Bologna University) Georgantopoulos (INAF-OABologna) P. Ranalli (Bologna University) F. Fiore (INAF-OARoma) M. Brusa (MPE) … many others …

Peak Energy ~ 29 keV HEAO1-PDS ~ 22 keV Swift NHXM, November 13, 2009

INTEGRAL & Swift (> 10 keV) --> a few (1-2)% Deep “soft” X-ray surveys have resolved some 80% of the XRB (below a few keV ) but “only” 50% > 6 keV INTEGRAL & Swift (> 10 keV) --> a few (1-2)% Wealth of X-ray and multi-wavelength follow-up available -> possible to estimate the “size” and “average spectrum” of the “missing” population Compton Thick AGN ? NHXM, November 13, 2009

Modelling 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. luminosity dependent 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

NHXM, November 13, 2009

~ 4 at low Log LX < 44 Luminosities ~ 1 at high Log LX > 44 Mildly (log NH =24-25) (NGC 6240, Circinus) Heavily (log NH >25) (NGC1068) ~ 4 at low Log LX < 44 Luminosities ~ 1 at high Log LX > 44 luminosities NHXM, November 13, 2009

Why bother ? The missing population may provide an important contribution to the BH mass function SMBH accretion rate, AGN vs. galaxy co-evolution… Different prescriptions for the details of luminosity and redshift dependence of fOBS Interesting for physics but little impact on models Every model has a lot of parameters which can be tuned and strong degeneracies especially at high energies where the resolved fraction is tiny . Claims on the properties of the missing population should be treated with caution High energy cut-offs (~100 keV) and radio-loud (Blazars)

Compton Thick AGN contribution in Gilli+07

Compton Thick in nearby Universe QSO2/QSO = 0.3 QSO2/QSO = 0.5 Treister+09 Decrease the fraction of obscured AGN at high luminosity wrt Gilli+07 At the expenses of a worse fit to the XRB spectrum at high energies 10% contribution from “flat” spectrum radio loud AGN (Blazars ?) <z> ~ 0 @ 10-11 <z> ~ 1 @ 10-15 NHXM, November 13, 2009

Compton Thick AGN at high redshift Several evidences Daddi+07 Fiore+08,09 Alexander+08 … for a large population of CT AGN at z ~ 2 +- 1 “Contamination” by SF galaxies or just mildly obscured may be an issue If nearby CT are “rare” while abundant at high z a stronger Cosmological evolution is implied Vignali+09 in prep

Scattering fraction < 0.5 % “Buried” AGN ? Ueda+07 Scattering fraction < 0.5 % NGC4992 Comastri+09 “Scattering” fraction is very low ( < 0.5 %) more examples in Eguchi+09 not related to Compton Thickness but rather to Reflection component “Buried” AGN (see also Winter+08) NHXM, November 13, 2009

4 X NHXM, November 13, 2009

Local Black Holes and AGN relics Marconi et al. 2004 have shown that local BHs are relics of AGN activity by comparing: the local BH mass function (from galaxy L/σ functions and MBH-Lbul/MBH-σe) the relic BHMF (from AGN luminosity function and continuity equation) Importance of AGN LF: even the hard (2-10 keV) XLF does not sample the whole AGN population. Heavily obscured Compton-thick AGN are missing ... Hard-X LF Soft-X LF Correction for CT from XRB models L = ε dM/dt c2 L = λ LE Qso LF NHXM, November 13, 2009

Radio loud and -ray background Giommi+06 Comastri+96 Ajello+09 Draper+09

High energy cut-off 100-400 keV Radio loud AGN / Blazars contribute some 10% to the soft XRB Normalizing to 1 keV for a range of slopes (0.5-0.7) a break or cut-off must be present around 1 MeV otherwise the soft -ray background would be exceeded High energy cut-off 100-400 keV NHXM, November 13, 2009

More peaked Narrower redshift distr.? Different sources ? Difference spectrum CT from GCH07 EC = 200 keV

Residuals assuming Swift = 10 kT ~ 8(1+z) keV Residuals assuming Swift best fit = 10 kT ~ 10(1+z) keV Saturated Comptonization = 10 kT ~ 10(1+z) keV Compton Thick in Gilli+07 z = 2 z ~ 0.6 z = 3 z ~ 0.8

60% to 80% of the hard 10-40 keV XRB will be resolved

Observational Strategy A spectral survey of local CT Seyfert 2 galaxies previously discovered by BeppoSAX, INTEGRAL Swift and Suzaku. This should be accompanied by a volume limited survey of IR-bright or OIII-bright or … galaxies which have not shown strong X-ray emission below 10 keV, to search for highly CT objects. A spectral survey of moderately obscured luminous QSOs discovered by XMM, Chandra up to z~1 (High luminosity) Deep observations to search for faint mildly CT AGN + serendipitous survey (high redshift) A survey of candidate CT AGN selected using their infrared emission (Spitzer/Herschel). NHXM, November 13, 2009

Polarimetric and Energetic Radiation Observatory a Legacy for Astrophysics PEROLA