We constrain the number density and evolution of Compton-thick Active Galactic Nuclei (AGN), and their contribution to the extragalactic X-ray background. In the local Universe we use the wide area surveys from the Swift and INTEGRAL satellites, while for high redshifts we explore candidate selections based on mid-IR parameters. We present the properties of a sample of 211 heavily-obscured AGN candidates in the Extended Chandra Deep Field-South (ECDF-S) selecting objects with f24/fR>1000 and R-K>4.5. The X-ray to mid-IR ratios for these sources are significantly larger than that of star-forming galaxies and ~2 orders of magnitude smaller than for the general AGN population, suggesting column densities of NH>5x10^24 cm^-2. The space density of CT AGN at z~2 derived from these observations is ~10^-5 Mpc^{-3}, finding a strong evolution in the number of LX>10^44 erg/s sources from z=1.5 to 2.5.
@article{arxiv.0912.2742,
title = {The Space Density of Compton-thick AGN},
author = {E. Treister and C. M. Urry and C. Cardamone and S. Virani and K. Schawinski and E. Gawiser},
journal= {arXiv preprint arXiv:0912.2742},
year = {2015}
}
Comments
4 pages, 3 figures, to appear in proceedings for 'X-ray Astronomy 2009', Bologna 09/2009, AIP Conference Series, Eds. A. Comastri, M. Cappi, L. Angelini; author list fixed