Chandra Observations of Heavily-Obscured AGN at z 2

Details Chandra Observations of Heavily-Obscured AGN at z 2 Chandra Observations of Heavily-Obscured AGN at z 2

Feb 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010head...11.3506t&link_type=abstract

American Astronomical Society, HEAD meeting #11, #35.06; Bulletin of the American Astronomical Society, Vol. 41, p.715

Astronomy and Astrophysics

Astrophysics

Scientific paper

We study the properties of a sample of 211 heavily-obscured Active Galactic Nucleus (AGN) candidates in the Extended Chandra Deep Field-South selecting objects with f24/fR>1000 and R-K>4.5. The stacked X-ray signal of the sample is strong, with an observed ratio of soft to hard X-ray counts consistent with a population of 90% heavily obscured AGN combined with 10% star-forming galaxies. The X-ray to mid-IR ratios for these sources are significantly larger than that of star-forming galaxies and 2 orders of magnitude smaller than for the general AGN population, suggesting column densities greater than 5x1024cm-2. This sample of heavily-obscured AGN candidates implies a space density at z 2 of 10-5Mpc-3, finding a strong evolution in the number of luminous sources from z=1.5 to 2.5. Such strong evolution was not predicted by any existing AGN luminosity function, but can be accurately explained by a simple prescription in which every new quasar is generated by the gas-rich merger of two massive galaxies, which is originally heavily obscured and after 100 Myrs removes most of the surrounding gas and dust to reveal an unobscured quasar.
Support for this work was provided by the National Aeronautics and Space Administration through Chandra Postdoctoral Fellowship Award Number PF8-90055 issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060.

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