The XXL Survey VI. The 1000 brightest X-ray point sources
Artikel i vetenskaplig tidskrift, 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.
STRUCTURE
WIDE-FIELD SURVEY
surveys
X-rays: general
ASTRONOMY & ASTROPHYSICS
P409
Astronomy & Astrophysics
GALAXY REDSHIFT
ACTIVE GALACTIC NUCLEI
P389
SURVEY
SUPERMASSIVE BLACK-HOLES
GIS CATALOG PROJECT
catalogs
MEDIUM-SENSITIVITY SURVEY
QUASAR
galaxies: active
RUCTURE
LUMINOSITY FUNCTION
NEWTON SERENDIPITOUS SURVEY
V132
EVOT ML
LARGE-SCALE
LARGE-AREA SURVEY
1984
V740
Författare
S. Fotopoulou
Universite de Geneve
F. Pacaud
Universitat Bonn
S. Paltani
Universite de Geneve
P. Ranalli
Lunds Universitet
National Observatory of Athens
M. E. Ramos-Ceja
Universitat Bonn
L. Faccioli
CEA Saclay
M. Plionis
National Observatory of Athens
Instituto Nacional de Astrofisica Optica y Electronica
Aristotle University of Thessaloniki
C. Adami
Laboratoire d'Astrophysique de Marseille
A. Bongiorno
Osservatorio Astronomico di Roma
M. Brusa
Osservatorio Astronomico Di Bologna
Alma Mater Studiorum Universita di Bologna
L. Chiappetti
INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan
S. Desai
Excellence Cluster Universe
Ludwig-Maximilians-Universitat Munchen
A. Elyiv
Main Astronomical Observatory Nasu
Alma Mater Studiorum Universita di Bologna
C. Lidman
Australian Astronomical Observatory
O. Melnyk
University of Zagreb
Taras Shevchenko National University of Kyiv
M. Pierre
CEA Saclay
E. Piconcelli
Osservatorio Astronomico di Roma
C. Vignali
Osservatorio Astronomico Di Bologna
Alma Mater Studiorum Universita di Bologna
S. Alis
Istanbul Universitesi
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
Universite de Geneve
L. Guennou
University of KwaZulu-Natal
Cathy Horellou
Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik
A. Iovino
Osservatorio Astronomico di Brera
E. Koulouridis
CEA Saclay
National Observatory of Athens
J. Liske
Universitat Hamburg
S. Maurogordato
Universite Nice Sophia Antipolis
F. Menanteau
University of Illinois at Urbana-Champaign
J. J. Mohr
Excellence Cluster Universe
Max Planck Institut fur extraterrestrische Physik
Ludwig-Maximilians-Universitat Munchen
M. Owers
Macquarie University
Australian Astronomical Observatory
B. Poggianti
Osservatorio Astronomico di Padova
E. Pompei
European Southern Observatory Santiago
T. Sadibekova
CEA Saclay
A. Stanford
UC Davis
R. Tuffs
Max Planck Institut fur Kernphysik
J. Willis
University of Victoria
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 592 A5 A5Ämneskategorier (SSIF 2011)
Astronomi, astrofysik och kosmologi
Fundament
Grundläggande vetenskaper
Infrastruktur
Onsala rymdobservatorium
DOI
10.1051/0004-6361/201527402