Searching for luminous absorbed sources in the WISE AGN catalogue

Abstract

Mid-IR colour selection techniques have proved to be very efficient in finding AGN. This is because the AGN heats the surrounding dust producing warm mid-IR colours. Using the WISE 3.6, 4.5 and 12 $\mu m$ colours, the largest sample of IR selected AGN has already been produced containing 1.4 million AGN over the whole sky. Here, we explore the X-ray properties of this AGN sample by cross-correlating it with the subsample of the 3XMM X-ray catalogue that has available X-ray spectra and at the same time optical spectroscopy from SDSS. Our goal is to find rare luminous obscured AGN. Our final sample contains 65 QSOs with $\log \nu {\mathrm{L}}_{\nu }\ge 46.2$\,erg\,s${}^{-1}$. This IR luminosity cut corresponds to $\log {\mathrm{L}}_{\mathrm{X}}\approx 45$\,erg\,s${}^{-1}$, at the median redshift of our sample ($z=2.3$), that lies at the bright end of the X-ray luminosity function at $z>2$. The X-ray spectroscopic analysis reveals seven obscured AGN having a column density ${\mathrm{N}}_{\mathrm{H}}>10^{22}\mathrm{c}{\mathrm{m}}^{-2}$. Six of them show evidence for broad [CIV] absorption lines and five are classified as BALQSOs. We fit the optical spectra of our X-ray absorbed sources to estimate the optical reddening. We find that none of these show any obscuration according to the optical continuum. These sources add to the growing evidence for populations of luminous QSOs with evidence for substantial absorption by outflowing ionised material, similar to those expected to be emerging from their absorbing cocoons in the framework of AGN/galaxy co-evolution.

10 pages, 5 figures, 3 Tables, MNRAS accepted

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• X-ray properties of dust-obscured galaxies with broad optical/UV emission lines
• Fast SMBH growth in the SPT2349--56 protocluster at $z=4.3$
• Forward modeling the multiwavelength properties of Active Galactic Nuclei: application to X-ray and WISE mid-infrared samples
• Obscuration properties of mid-IR selected AGN
• A search for X-ray absorbed sources in the 3XMM catalogue, using photometric redshifts and Bayesian spectral fits
• Harnessing the XMM-Newton data: X-ray spectral modelling of 4XMM-DR11 detections and 4XMM-DR11s sources