Book contents
Evolution of supermassive black holes
Published online by Cambridge University Press: 11 April 2011
Summary
The cosmological evolution of supermassive black holes (SMBHs) seems to be intimately linked to their host galaxies. Active galactic nuclei (AGN) can be probed by deep x-ray surveys. We review results from selected large x-ray samples including the first results from the XMM-Newton COSMOS survey. A new picture arises from the fact that high-luminosity AGN grow earlier than low-luminosity AGN. In particular, the space density of low-luminosity AGN exhibits a significant decline for redshifts above z = 1. This “anti-hierarchical” growth scenario of SMBHs can be explained by two modes of accretion with different efficiency. The population of Compton-thick sources plays a key role in our understanding of the BH growth history. Their space density and redshift distribution is relevant to estimate the SMBH mass function. A comparison with the relic SMBH mass distribution in the local Universe constrains the average radiative efficiency and Eddington ratio of the accretion. We discuss a new synthesis model of Compton-thin and Compton-thick sources that is in concordance with deep x-ray observations, and in particular predicts the right level of contribution of the Compton-thick source population observed in the Chandra Deep Field South observations as well as the first INTEGRAL and Swift catalogs of AGN. Currently, one of the most important problems is the evolution of obscuration with redshift.
Introduction
Deep surveys
Deep field observations are a suitable observational technique to probe AGN physics. In multi-wavelength campaigns, astronomers select a field in the sky and produce images from several pointings.
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- Black Holes , pp. 136 - 149Publisher: Cambridge University PressPrint publication year: 2011