Supermassive Black Holes in Deep Multiwavelength Surveys

TL;DR

Deep multiwavelength surveys have revealed that most supermassive black holes are obscured by gas and dust across various redshifts, with obscuration levels depending on luminosity and redshift, informing galaxy and black hole co-evolution.

Contribution

This paper synthesizes recent survey data to quantify the prevalence and obscuration of AGN across redshifts, highlighting the need for larger surveys at higher redshifts.

Findings

Most AGN are obscured at all redshifts.

Obscuration depends on luminosity and redshift.

Current surveys constrain AGN demographics up to z~2.

Abstract

In recent years deep X-ray and infrared surveys have provided an efficient way to find accreting supermassive black holes, otherwise known as active galactic nuclei (AGN), in the young universe. Such surveys can, unlike optical surveys, find AGN obscured by high column densities of gas and dust. In those cases, deep optical data show only the host galaxy, which can then be studied in greater detail than in unobscured AGN. Some years ago the hard spectrum of the X-ray "background" suggested that most AGN were obscured. Now GOODS, MUSYC, COSMOS and other surveys have confirmed this picture and given important quantitative constraints on AGN demographics. Specifically, we show that most AGN are obscured at all redshifts and the amount of obscuration depends on both luminosity and redshift, at least out to redshift z~2, the epoch of substantial black holes and galaxy growth. Larger-area deep infrared and hard X-ray surveys will be needed to reach higher redshifts and to probe fully the co-evolution of galaxies and black holes.