Supermassive black holes in deep multiwavelength surveys

Summary

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 fully probe the co-evolution of galaxies and black holes.

Cosmic growth of black holes and galaxies

Abundant evidence indicates that the growth of a supermassive black hole is closely tied to the formation and evolution of the surrounding galaxy. The energy released from accretion onto the black hole affects star formation in the galaxy, probably limiting growth at the high- and low-mass ends and, of course, the distribution and angular momentum of matter in the galaxy governs the amount of matter accumulated by the black hole (Silk & Rees 1998; King 2005; Rovilos et al. 2007).