The XXL Survey VI. The 1000 brightest X-ray point sources
Journal 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.

EVOT ML

surveys

ASTRONOMY & ASTROPHYSICS

GIS CATALOG PROJECT

SUPERMASSIVE BLACK-HOLES

STRUCTURE

SURVEY

P409

1984

V132

RUCTURE

LUMINOSITY FUNCTION

catalogs

GALAXY REDSHIFT

Astronomy & Astrophysics

ACTIVE GALACTIC NUCLEI

WIDE-FIELD SURVEY

LARGE-AREA SURVEY

P389

NEWTON SERENDIPITOUS SURVEY

QUASAR

X-rays: general

MEDIUM-SENSITIVITY SURVEY

LARGE-SCALE

galaxies: active

V740

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

Aristotle University of Thessaloniki

National Observatory of Athens

National Institute of Astrophysics, Optics and Electronics

C. Adami

Laboratoire d'Astrophysique de Marseille

A. Bongiorno

Osservatorio Astronomico di Roma

M. Brusa

Osservatorio Astronomico Di Bologna

University of Bologna

L. Chiappetti

INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan

S. Desai

Excellence Cluster Universe

Ludwig-Maximilians-Universität München

A. Elyiv

University of Bologna

Main Astronomical Observatory Nasu

C. Lidman

Australian Astronomical Observatory

O. Melnyk

Taras Shevchenko National University of Kyiv

University of Zagreb

M. Pierre

The French Alternative Energies and Atomic Energy Commission (CEA)

E. Piconcelli

Osservatorio Astronomico di Roma

C. Vignali

University of Bologna

Osservatorio Astronomico 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

University of Geneva

L. Guennou

University of KwaZulu-Natal

Cathy Horellou

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

A. Iovino

Osservatorio Astronomico di Brera

E. Koulouridis

The French Alternative Energies and Atomic Energy Commission (CEA)

National Observatory of Athens

J. Liske

Universität Hamburg

S. Maurogordato

Université Nice Sophia Antipolis (UNS)

F. Menanteau

University of Illinois

J. J. Mohr

Excellence Cluster Universe

Ludwig-Maximilians-Universität München

Max Planck Society

M. Owers

Macquarie University

Australian Astronomical Observatory

B. Poggianti

Osservatorio Astronomico di Padova

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 A5

Subject Categories

Astronomy, Astrophysics and Cosmology

Roots

Basic sciences

Infrastructure

Onsala Space Observatory

DOI

10.1051/0004-6361/201527402

More information

Latest update

9/6/2018 1