The XMM-Newton Wide Angle Survey (XWAS)

Abstract

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. 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 performed at the Anglo Australian Telescope Two Degree Field were analysed, and the derived spectra were classified based on optical emission lines. We have identified through optical spectroscopy 940 X-ray sources over ~11.8 deg^2 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 likely to be present also 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. Due 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 to further study subsamples and particular cases. The overall properties of the extragalactic objects are presented in this paper.

Accepted for publication in A&A, 12 pages, 11 figures

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