Paper: astro-ph/0505486
Date: Tue, 24 May 2005 09:14:07 GMT (61kb)

Title: Most supermassive black hole growth is obscured by dust

Authors: Alejo Martinez-Sansigre, Steve Rawlings, Mark Lacy, Dario Fadda,
Francine R. Marleau, Chris Simpson, Chris J. Willott, Matt J. Jarvis
Comments: To appear in Nature. Supplementary Information can be found at
http://www-astro.physics.ox.ac.uk/~ams/
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Supermassive black holes underwent periods of exponential growth which are
observed as quasars in the distant Universe. The summed emission from these
quasars generates the cosmic X-ray background, the spectrum of which has been
used to argue that most black-hole growth is obscured. There are clear examples
of obscured black-hole growth in the form of `Type-2' quasars, but their
numbers are fewer than expected from modelling of the X-ray background. Here we
report on the direct detection of a population of distant `Type-2' quasars
which is at least comparable in size to the well-known unobscured Type-1
population. This population was found by selecting objects whose mid-infrared
and radio emissions are characteristic of quasars, but which are faint at
near-infrared and optical wavelengths. This population is responsible for most
of the black hole growth in the young Universe and, throughout cosmic history,
black-hole growth occurs in the dusty, gas-rich centres of active galaxies.

\\ ( http://arXiv.org/abs/astro-ph/0505486 , 61kb)