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.

X-rays: general

ASTRONOMY & ASTROPHYSICS

galaxies: active

ACTIVE GALACTIC NUCLEI

STRUCTURE

NEWTON SERENDIPITOUS SURVEY

MEDIUM-SENSITIVITY SURVEY

GIS CATALOG PROJECT

SUPERMASSIVE BLACK-HOLES

RUCTURE

surveys

QUASAR

SURVEY

LUMINOSITY FUNCTION

P389

LARGE-AREA SURVEY

WIDE-FIELD SURVEY

catalogs

GALAXY REDSHIFT

V132

1984

P409

V740

LARGE-SCALE

EVOT ML

Astronomy & Astrophysics

Författare

S. Fotopoulou

Universite de Geneve

F. Pacaud

Universität Bonn

S. Paltani

Universite de Geneve

P. Ranalli

National Observatory of Athens

Lunds universitet

M. E. Ramos-Ceja

Universität Bonn

L. Faccioli

Le Commissariat à l’énergie atomique et aux énergies alternatives (CEA)

M. Plionis

Aristotle University of Thessaloniki

Instituto Nacional de Astrofisica Optica y Electronica

National Observatory of Athens

C. Adami

Laboratoire d'Astrophysique de Marseille

A. Bongiorno

Osservatorio Astronomico di Roma

M. Brusa

Osservatorio Astronomico Di Bologna

Universita di Bologna

L. Chiappetti

INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan

S. Desai

Excellence Cluster Universe

Ludwig-Maximilians-Universität München

A. Elyiv

Universita di Bologna

Main Astronomical Observatory Nasu

C. Lidman

Australian Astronomical Observatory

O. Melnyk

Sveučilište u Zagrebu

Taras Shevchenko National University of Kyiv

M. Pierre

Le Commissariat à l’énergie atomique et aux énergies alternatives (CEA)

E. Piconcelli

Osservatorio Astronomico di Roma

C. Vignali

Osservatorio Astronomico Di Bologna

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

National Observatory of Athens

Le Commissariat à l’énergie atomique et aux énergies alternatives (CEA)

J. Liske

Universität Hamburg

S. Maurogordato

Universite Nice Sophia Antipolis

F. Menanteau

University of Illinois at Urbana-Champaign

J. J. Mohr

Max Planck-institutet

Excellence Cluster Universe

Ludwig-Maximilians-Universität München

M. Owers

Macquarie University

Australian Astronomical Observatory

B. Poggianti

Osservatorio Astronomico di Padova

E. Pompei

European Southern Observatory Santiago

T. Sadibekova

Le Commissariat à l’énergie atomique et aux énergies alternatives (CEA)

A. Stanford

UC Davis

R. Tuffs

Max Planck-institutet

J. Willis

University of Victoria

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 592 A5

Ämneskategorier

Astronomi, astrofysik och kosmologi

Fundament

Grundläggande vetenskaper

Infrastruktur

Onsala rymdobservatorium

DOI

10.1051/0004-6361/201527402