The XXL Survey VI. The 1000 brightest X-ray point sources
Review article, 2016
Context. X-ray extragalactic surveys are ideal laboratories for the study of the evolution and clustering of active galactic nuclei (AGN). Usually, a combination of deep and wide surveys is necessary to create a complete picture of the population. Deep X-ray surveys provide the faint population at high redshift, while wide surveys provide the rare bright sources. Nevertheless, very wide area surveys often lack the ancillary information available for modern deep surveys. The XXL survey spans two fields of a combined 50 deg(2) observed for more than 6Ms with XMM-Newton, occupying the parameter space that lies between deep surveys and very wide area surveys; at the same time it benefits from a wealth of ancillary data. Aims. This paper marks the first release of the XXL point source catalogue including four optical photometry bands and redshift estimates. Our sample is selected in the 2-10 keV energy band with the goal of providing a sizable sample useful for AGN studies. The limiting flux is F2-10 keV = 4.8 x 10(14) erg s(-1) cm(-2). Methods. We use both public and proprietary data sets to identify the counterparts of the X-ray point-like sources by means of a likelihood ratio test. We improve upon the photometric redshift determination for AGN by applying a Random Forest classification trained to identify for each object the optimal photometric redshift category (passive, star forming, starburst, AGN, quasi-stellar objects (QSO)). Additionally, we assign a probability to each source that indicates whether it might be a star or an outlier. We apply Bayesian analysis to model the X-ray spectra assuming a power-law model with the presence of an absorbing medium. Results. We find that the average unabsorbed photon index is
= 1.85 +/- 0.40 while the average hydrogen column density is log
i = 21.07 +/- 1.2 cm(-2). We find no trend of Gamma or N-H with redshift and a fraction of 26% absorbed sources (log N-H > 22) consistent with the literature on bright sources (log L-x > 44). The counterpart identification rate reaches 96.7% for sources in the northern field, 97.7% for the southern field, and 97.2% in total. The photometric redshift accuracy is 0.095 for the full XMM-XXL with 28% catastrophic outliers estimated on a sample of 339 sources. Conclusions. We show that the XXL-1000-AGN sample 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.
V132
ASTRONOMY & ASTROPHYSICS
catalogs
MEDIUM-SENSITIVITY SURVEY
SUPERMASSIVE BLACK-HOLES
STRUCTURE
LUMINOSITY FUNCTION
P389
P409
QUASAR
1984
SURVEY
EVOT ML
V740
ACTIVE GALACTIC NUCLEI
surveys
WIDE-FIELD SURVEY
GIS CATALOG PROJECT
X-rays: general
RUCTURE
LARGE-AREA SURVEY
NEWTON SERENDIPITOUS SURVEY
Astronomy & Astrophysics
LARGE-SCALE
galaxies: active
GALAXY REDSHIFT
Author
S. Fotopoulou
University of Geneva
F. Pacaud
University of Bonn
S. Paltani
University of Geneva
P. Ranalli
National Observatory of Athens
Lund University
M. E. Ramos-Ceja
University of Bonn
L. Faccioli
The French Alternative Energies and Atomic Energy Commission (CEA)
M. Plionis
National Observatory of Athens
National Institute of Astrophysics, Optics and Electronics
Aristotle University of Thessaloniki
C. Adami
Laboratoire d'Astrophysique de Marseille
A. Bongiorno
Osservatorio Astronomico di Roma
M. Brusa
Istituto nazionale di astrofisica (INAF)
University of Bologna
L. Chiappetti
Istituto nazionale di astrofisica (INAF)
S. Desai
Ludwig Maximilian University of Munich (LMU)
A. Elyiv
Main Astronomical Observatory Nasu
University of Bologna
C. Lidman
Australian Astronomical Observatory
O. Melnyk
University of Zagreb
Taras Shevchenko National University of Kyiv
M. Pierre
The French Alternative Energies and Atomic Energy Commission (CEA)
E. Piconcelli
Osservatorio Astronomico di Roma
C. Vignali
Istituto nazionale di astrofisica (INAF)
University of Bologna
S. Alis
Istanbul University
F. Ardila
University of Florida
S. Arnouts
Laboratoire d'Astrophysique de Marseille
I. Baldry
Liverpool John Moores University
M. Bremer
University of Bristol
D. Eckert
University of Geneva
L. Guennou
University of KwaZulu-Natal
Cathy Horellou
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
A. Iovino
Istituto nazionale di astrofisica (INAF)
E. Koulouridis
National Observatory of Athens
The French Alternative Energies and Atomic Energy Commission (CEA)
J. Liske
University of Hamburg
S. Maurogordato
Université Nice Sophia Antipolis (UNS)
F. Menanteau
University of Illinois
J. J. Mohr
Ludwig Maximilian University of Munich (LMU)
Max Planck Society
M. Owers
Australian Astronomical Observatory
Macquarie University
B. Poggianti
Istituto nazionale di astrofisica (INAF)
E. Pompei
European Southern Observatory Santiago
T. Sadibekova
The French Alternative Energies and Atomic Energy Commission (CEA)
A. Stanford
University of California
R. Tuffs
Max Planck Society
J. Willis
University of Victoria
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 592 A5 A5Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Roots
Basic sciences
Infrastructure
Onsala Space Observatory
DOI
10.1051/0004-6361/201527402