[AGN, Quasars, Black Holes -- Oral ]

New Perspectives on Compton-thick AGN

Tahir Yaqoob, Johns Hopkins University
Kendrah Murphy (MIT, Kavli Institute)

Obscured AGN are now recognized as playing a major role in the population of accreting supermassive black holes. We present new results from theoretical calculations that reveal some rather surprising characteristics of Compton-thick AGN. Our findings have a direct impact on the interpretation of existing data, as well as data from the upcoming missions NuSTAR and Astro-H. We show calculations of the dependence of the Fe K line EW, flux, and observed to intrinsic continuum luminosity ratios on the reprocessor column density, geometry, and orientation. We find that, whilst a large EW Fe K emission line is traditionally thought to be a hallmark for identifying Compton-thick AGN, there is a large part of parameter space in which the Fe K line may not even be detectable due to a small EW. We also show that the soft and hard reprocessed X-ray continua differ significantly from those based on models that are currently used to deduce column density distributions of AGN found in surveys, such as those with Chandra, XMM, and the Swift-BAT. The origin of the differences can be attributed to the inclusion of more realistic assumptions in our models compared to those currently in use. These results also impact synthesis models of the CXRB since our model can be used to derive more realistic column density distributions for AGN. The intrinsic continuum luminosity in Compton-thick AGN is a critical quantity that cannot be directly measured and there is no proxy for estimating it in a trivial manner. However, we show how a robust lower limit on the intrinsic luminosity may be inferred. When applied to Swift-BAT AGN, our calculations show that the BAT survey is actually more biased towards Compton-thick type 1 AGN than Compton-thin type 2 OR type 1 AGN.