A Joint Model of X-Ray and Infrared Backgrounds. II. Compton-thick Active Galactic Nucleus Abundance

November 2013 • 2013ApJ...777....6S

Authors • Shi, Yong • Helou, George • Armus, Lee

Abstract • We estimate the abundance of Compton-thick (CT) active galactic nuclei (AGNs) based on our joint model of X-ray and infrared backgrounds. At L _{rest2-10 keV} > 10⁴² erg s^-1, the CT AGN density predicted by our model is a few ×10^-4 Mpc^-3 from z = 0 up to z = 3. CT AGNs with higher luminosity cuts (>10⁴³, 10⁴⁴, and 10⁴⁵ erg s^-1) peak at higher redshift and show a rapid increase in number density from z = 0 to z ~ 2-3. The CT AGN to all AGN ratio appears to be low (2%-5%) at f _{2-10 keV} > 10^-15 erg s^-1 cm^-2 but rises rapidly toward fainter flux levels. The CT AGNs account for ~38% of the total accreted supermassive black hole mass and contribute ~25% of the cosmic X-ray background spectrum at 20 keV. Our model predicts that the majority (90%) of luminous and bright CT AGNs (L _rest2-10keV > 10⁴⁴ erg s^-1 or f _{2-10 keV} > 10^-15 erg s^-1 cm^-2) have detectable hot dust 5-10 μm emission, which we associate with a dusty torus. The fraction drops for fainter objects, to around 30% at L _{rest2-10 keV} > 10⁴² erg s^-1 or f _{2-10 keV} > 10^-17 erg s^-1 cm^-2. Our model confirms that heavily obscured AGNs (N _{H I} > 10²³ cm^-2) can be separated from unobscured and mildly obscured ones (N _{H I} < 10²³ cm^-2) in the plane of observed frame X-ray hardness versus mid-IR/X-ray ratio.

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Links

• PREPRINT http://arxiv.org/abs/1309.1202
• ELECTR https://doi.org/10.1088%2F0004-637X%2F777%2F1%2F6
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2013ApJ...777....6S
• PDF https://iopscience.iop.org/article/10.1088/0004-637X/777/1/6/pdf
• PDF https://stacks.iop.org/0004-637X/777/6/pdf
• DATA https://irsa.ipac.caltech.edu/bibdata/2013/S/2013ApJ...777....6S.html