Obscuration properties of mid-IR selected AGN

Abstract

The goal of this work is to study the obscuration properties of mid-infrared (mid-IR) selected AGN. For that purpose, we use {\it{WISE}} sources in the Stripe 82-XMM area to identify mid-IR AGN candidates, applying the Assef et al. criteria. Stripe 82 has optical photometry $\approx$\,2 times deeper than any single-epoch SDSS region. XMM-Newton observations cover $\sim$26\,deg${}^2$. Applying the aforementioned criteria, 1946 IR AGN are selected. $\sim 78\%$ have SDSS detection, while 1/3 of them is detected in X-rays, at a flux limit of $\sim 5\times 10^{-15}\mathrm{erg}{\mathrm{s}}^{-1}\mathrm{c}{\mathrm{m}}^{-2}$. Our final sample consists of 507 IR AGN with X-ray detection and optical spectra. Applying a $\mathrm{r}-W2>6$ colour criterion, we find that the fraction of optically red AGN drops from 43\% for those sources with SDSS detection to $23\%$ for sources that also have X-ray detection. X-ray spectral fitting reveals 40 ($\sim 8\%$) X-ray absorbed AGN (${\mathrm{N}}_{\mathrm{H}}>10^{22}\mathrm{c}{\mathrm{m}}^{-2}$). Among the X-ray unabsorbed AGN, there are 70 red systems. To further investigate the absorption of these sources, we construct Spectral Energy Distributions (SEDs) for the total IR AGN sample. SED fitting reveals that $\sim 20\%$ of the optically red sources have such colours because the galaxy emission is a primary component in the optical part of the SED, even though the AGN emission is not absorbed at these wavelengths. SED fitting also confirms that $12\%$ of the X-ray unabsorbed, IR AGN are optically obscured.

MNRAS accepted, 10 pages, 8 figures

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Cited by in corpus (8)

• On the cosmic evolution of AGN obscuration and the X-ray luminosity function: XMM-Newton and Chandra spectral analysis of the 31.3 deg${}^2$ Stripe 82X
• Galaxy properties of type 1 and 2 X-ray selected AGN and comparison among different classification criteria
• The eROSITA Final Equatorial-Depth Survey (eFEDS): A multiwavelength view of WISE mid-infrared galaxies/active galactic nuclei
• AGN X-ray luminosity function and absorption function in the Early Universe ($3\le z\le 6$)
• Mid-infrared Variability of Low-redshift Active Galactic Nuclei : Constraints on a Hot Dust Component with a Variable Covering Factor
• A search for X-ray absorbed sources in the 3XMM catalogue, using photometric redshifts and Bayesian spectral fits
• Central radio galaxies in galaxy clusters: Joint surveys by eROSITA and ASKAP
• AGN obscuration in optical and X-rays: Host properties and the interplay of nuclear and galactic gas and dust in a combined SDSS-XMM sample