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Free keywords:
Astrophysics, Galaxy Astrophysics, astro-ph.GA,Astrophysics, Cosmology and Extragalactic Astrophysics, astro-ph.CO
MPINP:
Infrarot-Astrophysik - Abteilung Hofmann
Abstract:
X-ray extragalactic surveys are ideal laboratories for the study of the
evolution and clustering of active galactic nuclei (AGN). The XXL Survey spans
two fields of a combined 50 $deg^2$ observed for more than 6Ms with XMM-Newton,
occupying the parameter space between deep surveys and very wide area surveys;
at the same time it benefits from a wealth of ancillary data. This paper marks
the first release of the XXL point source catalogue selected in the 2-10 keV
energy band with limiting flux
$F_{2-10keV}=4.8\cdot10^{-14}\rm{erg\,s^{-1}\,cm^{-2}}$. We use both public and
proprietary data sets to identify the counterparts of the X-ray point-like
sources and improved upon the photometric redshift determination for AGN by
applying a Random Forest classification trained to identify for each object the
optimal photometric redshift model library. We also assign a probability to
each source to be a star or an outlier. We model with Bayesian analysis the
X-ray spectra assuming a power-law model with the presence of an absorbing
medium. We find an average unabsorbed photon index of $\Gamma=1.85$ and average
hydrogen column density $\log{N_{H}}=21.07 cm^{-2}$. We find no trend of
$\Gamma$ or $N_H$ with redshift and a fraction of 26% absorbed sources ($\log
N_{H}>22$). We show that the XXL-1000-AGN number counts extended the number
counts of the COSMOS survey to higher fluxes and are fully consistent with the
Euclidean expectation. We constrain the intrinsic luminosity function of AGN in
the 2-10 keV energy band where the unabsorbed X-ray flux is estimated from the
X-ray spectral fit up to z=3. Finally, we demonstrate the presence of a
supercluster size structure at redshift 0.14, identified by means of
percolation analysis of the XXL-1000-AGN sample. The XXL survey, reaching a
medium flux limit and covering a wide area is a stepping stone between current
deep fields and planned wide area surveys.
