Obscured quasars at redshift z ~ 2

Abstract

Completing the census of AGN in the Universe is the key to understanding the cosmic evolution of supermassive black holes (SMBH) and galaxies, and to resolving the spectrum of the X-ray background (XRB). However, a large population of AGN, especially the heavily obscured, Compton-thick AGN, are still missing from even the deepest X-ray surveys. The infrared spectra energy distribution (SED) of distant star-forming galaxies can reveal the presence of bright AGN activity. Using some of the deepest infrared, X-ray and radio data available in the GOODS fields, we identify a population of infrared bright quasars at redshift z ~ 2, which are often missed in the X-ray band. Amongst these sources the number of obscured and heavily-obscured quasars is much higher than those previously found in several X-ray and optical selected samples. A unique view on these heavily-obscured quasars is now given at high energies by NuSTAR. I will present the first NuSTAR detection of a heavily obscured quasar at z 2. This source is a potential archetype of the heavily-obscured high-z AGN in which most of the black hole growth is happening, that can explain the mysterious missing fraction of the XRB.