The XMM-Newton Wide Angle Survey (XWAS) ^⋆

¹ Centro de Astrobiología (INTA-CSIC), ESAC Campus, PO Box 78, 28691 Villanueva de la Cañada, Spain
e-mail: pilar.esquej@cab.inta-csic.es
² Dept. of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
³ Instituto de Física de Cantabria (CSIC-UC), Avda. de los Castros, 39005 Santander, Spain
⁴ Departamento de Física Moderna, Universidad de Cantabria, Avda. de Los Castros, 39005 Santander, Spain
⁵ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
⁶ INAF – Osservatorio Astronomico di Brera, via Brera 28, 20121 Milan, Italy
⁷ SRON – Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁸ European Southern Observatory, Karl-Schwarzschild-Stra β e 2, 85748 Garching bei München, Germany
⁹ University of California, San Diego, Center for Astrophysics & Space Sciences, 9500 Gilman Drive, CA 92093-0424, USA
¹⁰ Leibniz-Institute for Astrophysics Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹¹ Instituto Astrofísico de Canarias, (IAC), C/Vía Láctea, s/n, 38205 La Laguna, Tenerife, Spain

Received: 17 January 2012
Accepted: 18 February 2013

Abstract

Aims. This programme is aimed at obtaining one of the largest X-ray selected samples of identified active galactic nuclei to date in order to characterise such a population at intermediate fluxes, where most of the Universe’s accretion power originates. We present the XMM-Newton Wide Angle Survey (XWAS), a new catalogue of almost a thousand X-ray sources spectroscopically identified through optical observations.

Methods. A sample of X-ray sources detected in 68 XMM-Newton pointed observations was selected for optical multi-fibre spectroscopy. Optical counterparts and corresponding photometry of the X-ray sources were obtained from the SuperCOSMOS Sky Survey. Candidates for spectroscopy were initially selected with magnitudes down to R ~ 21, with preference for X-ray sources having a flux F_{0.5−4.5 keV} ≥ 10^-14 erg s^-1 cm^-2. Optical spectroscopic observations were made using the Two Degree Field of the Anglo Australian Telescope, and the resulting spectra were classified based on optical emission lines.

Results. We have identified through optical spectroscopy 940 X-ray sources over Ω ~ 11.8 deg² of the sky. Source populations in our sample can be summarised as 65% broad line active galactic nuclei (BLAGN), 16% narrow emission line galaxies (NELGs), 6% absorption line galaxies (ALGs) and 13% stars. An active nucleus is also likely to be present in the large majority of the X-ray sources spectroscopically classified as NELGs or ALGs. Sources lie in high-galactic latitude (|b| > 20 deg) XMM-Newton fields mainly in the southern hemisphere. Owing to the large parameter space in redshift (0 ≤ z ≤ 4.25) and flux (10^-15 ≤ F_{0.5 − 4.5 keV} ≤ 10^-12 erg s^-1 cm^-2) covered by the XWAS this work provides an excellent resource for the further study of subsamples and particular cases. The overall properties of the extragalactic objects are presented in this paper. These include the redshift and luminosity distributions, optical and X-ray colours and X-ray-to-optical flux ratios.