Dependence of clustering of X-ray AGN on obscuration. Issue 3 (6th September 2018)

• Record Type: Journal Article
• Authors: Koutoulidis, L; Georgantopoulos, I; Mountrichas, G; Plionis, M; Georgakakis, A; Akylas, A; Rovilos, E
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 481:Issue 3(2018)
• Page Start: 3063
• Page End: 3069
• Publication Date: 2018-09-06
• Subjects: galaxies: active -- X-rays: galaxies; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty2429
• Languages: English
• ISSNs: 0035-8711

Abstract

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 $\rm \mathit{ N}_H=10^{22}\, cm^{-2}$, 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 ($\rm \mathit{ r}_o= 7.0 \pm 0.6$ h −1 Mpc) compared to that of unobscured sources ($\rm \mathit{ r}_o= 5.4 \pm 0.6$ 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 $R-[4.5]\gt 6.1$ 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.