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"The environment of AGN at z~1"
Dr. Antonis Georgakakis
Imperial College, UK

When:  Thursday 19 April 2007 at 1:30pm
Where: 2nd Floor Seminar Room

Abstract:

The formation and evolution of AGN likely depends strongly on their
local density over Mpc scales.  Despite significant observational
progress however, the link between environment and black-hole
accretion remains controversial, especially at z~1, close to the peak
of the AGN luminosity density in the Universe.

I will present new results on the environment of X-ray selected AGN at
z~1 using data from the All-wavelength Extended Groth strip
International Survey (AEGIS), which includes deep (200ks per field)
wide-area (0.5deg2) Chandra observations and extensive optical
spectroscopy (9000 redshifts) to R~24mag.  Unlike previous efforts
that primarily use correlation function analysis to quantify the large
scale structure of AGN, we exploit the redshift information to map the
distribution of galaxies in 3-D across the surveyed area and to
measure the local density in the vicinity of X-ray sources.

Our analysis is robust against cosmic variance biases and shows, for
the first time, that X-ray selected AGN at z~1 avoid underdense
regions and that they are systematically associated with relatively
rich environments (group or cluster).  Also, AGN are not biased
relative to galaxies.  Their local densities are, on average, similar
to those of optically selected samples of the same rest-frame colour
(U-B) and optical luminosity (M_B).  These results at z~1 will be
compared against local studies that use the SDSS survey to assess the
typical environment of AGN at z~0.1 They will be also discussed in the
context of recent AGN formation models, which include feedback
mechanisms, and invoke either galaxy mergers (e.g. Hopkins et
al. 2005) or gas infall on the central galaxy of groups or clusters
(e.g. Croton et al. 2006) to drive material to the central galaxy
regions and to feed the black hole.

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