Hard X-ray AGN and the Cosmic X-ray Background Sergey Sazonov Space Research Institute, Moscow, Russia 1 Rome, Oct. 17, 2013
Plan Cosmic X-ray background: measurements, modeling and implications for heavily obscured AGN Properties of the local AGN population: hard X-ray infrared connection, observed and intrinsic fraction of strongly absorbed sources Conclusions and implications for future observations Rome, Oct. 17, 2013 2
CXB = integrated emission of AGN Uncertainties in modeling: CXB spectrum AGN spectral shape AGN redshift evolution CT AGN Gilli et al. 2007 A lot of Compton-thick quasars needed? Rome, Oct. 17, 2013 3
CXB-Earth observations by INTEGRAL in 2006 Churazov et al. 2007
Revnivtsev et al. 2003, Churazov et al. 2007
Ajello et al. 2008
Moretti et al. 2009
Updated CXB modeling Akylas et al. 2012 Treister et al. 2009 Substantial contribution from Compton-thick sources is not evident Rome, Oct. 17, 2013 8
Average hard X-ray spectrum of local AGN 11 AGN S=AE -1.62±0.03 e -E/(240±30)keV S=AE -1.73±0.09 e -E/(240±100)keV 7-year INTEGRAL sample (Krivonos et al. 2010) Simple stacking: S=Σf i 20 AGN S=AE -1.46 ±0.11 e -E/(88±20)keV 120 AGN Sazonov et al. 2008, Sazonov et al. 2010
Space density-weighted sum: S=ΣL i /V max,i We thus determine both the spectral shape and the total volume emissivity of the local AGN S=AE -1.93 S=AE -1.56 e-e/120 kev Red. χ 2 =2.05 (4 dof) 1.03 (3 dof) Sazonov et al. 2008, Sazonov et al. 2010
Evolution of AGN X-ray luminosity density Chandra Barger et al. 2005
Convolution of local AGN spectrum with z-dependence CXB ε ~ 1/z at z>1 ε = const at z>1 Consistent (within large uncertainties) with the CXB spectrum
Ricci et al. 2011 Vasudevan et al. 2013 Rome, Oct. 17, 2013 13
What would we like to know about AGN? Accretion physics Distribution of energy between accretion disk and hot corona What is the torus? Opening angle, optical depth, physical size History of supermassive black hole growth Rome, Oct. 17, 2013 14
Тор Диск Корона Bolometric luminosity is distributed between: Medium IR Optical UV (Type 1 AGN) X-ray gamma SS, Ostriker & Sunyaev 2004 Problems: Peak of energy release is in the far UV: absorption along the line of sight Variability: non-simultaneity of observations in different energy bands Rome, Oct. 17, 2013 15
AGN statistics N H We would like to fill this space z L bol Hard X-ray and mid-ir surveys are the best Rome, Oct. 17, 2013 16
AGN studies in the local Universe: INTEGRAL all-sky survey (17-60 kev) 3.5-year survey (2002-2006): 68 Seyferts and QSOs ( b >5 o ) Krivonos 2007; Sazonov et al. 2007, 2008 7-year survey (2002-2009): 150 Seyferts and QSOs ( b >5 o ) Krivonos 2010a, 2010b; Sazonov et al. 2010 Rome, Oct. 17, 2013 17
Hard X-ray luminosity function z<0.1 z>0.1 All: Log(L * )=43.56±0.18 γ 1 =0.81±0.11, γ 2 =2.28±0.14 z<0.1: Log(L * )=43.76±0.19 γ 1 =0.88±0.11, γ 2 =2.74±0.37 Rome, Oct. 17, 2013 18
Absorption column distribution 45% - unabsorbed (N H <10 22 ) 46% - weakly absorbed (10 22 < N H < 10 24 ) 9% - strongly absorbed (N H >10 24 ) Rome, Oct. 17, 2013 19
Fraction of obscured AGN as a function of luminosity Receding torus? Ω Torus /4π 1-0.25(log L 17-60 kev -41.5) Rome, Oct. 17, 2013 20
Swift/BAT 3-year survey Burlon et al. 2011 Rome, Oct. 17, 2013 21
IR observations of AGN from the 3.5- year INTEGRAL survey AGN AGN + starburst Spitzer Sazonov et al. 2012 Rome, Oct. 17, 2013 22
Correlation between hard X-ray and mid-ir emission INTEGRAL-Spitzer 68 AGN at z < 0.1 L MIR ~ L HX 0.74±0.06 Rome, Oct. 17, 2013 23
Disk vs. Torus Torus solid angle decreases with luminosity: Ω Torus /4π 1 0.25(log L HX - 41.5) (IR) Luminosity of the torus: L Torus = (Ω Torus /4π) L Disk (UV) luminosity of the disk: L Disk = (4π/Ω Torus ) L Torus Rome, Oct. 17, 2013 24
Disk vs. Corona L Disk 1.6 L Corona 0.97±0.06 Thus, the luminosities of disk and corona are similar Rome, Oct. 17, 2013 25
Bolometric corrections Hard X-ray luminosity is a good proxy of the bolometric luminosity for AGN with L 17-60 kev ~ 10 42 to 10 44.5 erg/s: L bol 10 L 17-60 kev Hence, absorption corrected X-ray luminosity is a good proxy too: L bol ~ 10 L 2-10 kev Mid-infrared luminosity: L bol ~ 5 L 15 μm but there is a non-linear dependence Rome, Oct. 17, 2013 26
Fraction of heavily obscured AGN =? Compton-thick sources Rome, Oct. 17, 2013 27
Heavily obscured AGN in the INTEGRAL sample IGR J16351-5806=ESO 137-G34 XMM IBIS Using X-ray data for such objects, one can estimate N H or show that N H > 10 25 (reflection dominates) Malizia al. 2009 Rome, Oct. 17, 2013 28
Propagation of hard X-rays through Torus Rome, Oct. 17, 2013 29
AGN-1 AGN-2 Rome, Oct. 17, 2013 30
Observed flux as a function of direction and N H Rome, Oct. 17, 2013 31
Average influence on AGN-1 and AGN-2 luminosities AGN-1 AGN-2 Rome, Oct. 17, 2013 32
True (absorption-corrected) hard X-ray luminosity function of local AGN Assumptions: Torus opening angle θ=45 o In AGN-1s, N H =10 24 Two main effects : AGN-1 (67) move to the left Heavily obscured AGN-2 (13) move to the right Emitted luminosity Each AGN gives its own estimate of AGN space density (1/V max ) -> large errors Rome, Oct. 17, 2013 33
Intrinsic dependence of obscured AGN fraction (torus opening angle) on luminosity Rome, Oct. 17, 2013 34
Perhaps, no discrepancy with IR/radio selected samples? Lawrence & Elvis 2010 Rome, Oct. 17, 2013 35
Conclusions Cosmic X-ray background does not provide stringent constraints on the abundance of heavily obscured AGN in the Universe Hard X-ray luminosity of the hot corona is comparable to the UV luminosity of the accretion disk in AGN > constraints on accretion models Hard X-ray luminosity is a good proxy of AGN bolometric luminosity -> good for reconstructing SMBH growth history using large surveys Measured fraction of absorbed AGN decreases with luminosity > indication of increasing opening angle of the torus However, when corrected for the observational bias, the fraction of obscured AGN does not show significant dependence on luminosity We need larger samples of hard X-ray selected AGN perhaps in combination with mid-ir data Rome, Oct. 17, 2013 36
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Hasinger 2008 Rome, Oct. 17, 2013 38
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