Dependence of clustering of X-ray AGN on obscuration
Abstract
Recent studies which select active galactic nucleus (AGN) in the mid-infrared (IR) part of the spectrum find that obscured AGNs reside in more massive dark matter haloes compared to unobscured ones. In contrast, X-ray AGN surveys do not find a difference in the dark matter haloes of these two populations. We visit anew this issue by examining the clustering properties of a large X-ray sample distributed over five deep fields. These are the CDF-N, CDF-S, ECDF-S, COSMOS, and AEGIS Chandra fields spanning the redshift interval 0.6 < z < 1.4. In particular, we present the clustering properties of 736 and 720 unobscured and obscured X-ray-selected AGNs (0.5-8 keV) with column densities higher and lower than N_H=10^{22} cm^{-2}, respectively. We perform a spatial correlation function analysis for the two samples, and we find a weak (2σ) difference in the clustering of obscured sources (r_o= 7.0 ± 0.6 h-1 Mpc) compared to that of unobscured sources (r_o= 5.4 ± 0.6 h-1 Mpc) using a fixed slope of γ = 1.8. Furthermore, we compare our findings with recent results that base the obscured and unobscured AGN classification on the optical/IR colour (R-[4.5]=6.1). We find that the optical/IR criterion fails to identify a purely AGN sample. In particular, reddened AGNs with R-[4.5]> 6.1 are divided almost equally between X-ray obscured and unobscured AGNs. Derivation of the spectral energy distributions reveals that in many cases the host galaxy contaminates the mid-IR bands thus affecting the optical/mid-IR obscured AGN classification.
- Publication:
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Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 2018
- DOI:
- 10.1093/mnras/sty2429
- Bibcode:
- 2018MNRAS.481.3063K
- Keywords:
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- galaxies: active;
- X-rays: galaxies