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The Chandra COSMOS-Legacy Survey: Source X-Ray Spectral Properties

Journal
Date Issued
2016
Author(s)
•
•
Civano, F.
•
Iwasawa, K.
•
Suh, H.
•
•
Zamorani, G.
•
•
Griffiths, R.
•
Miyaji, T.
•
Ranalli, P.
•
Salvato, M.
•
Schawinski, K.
•
Silverman, J.
•
Treister, E.
•
Urry, C. M.
•
Vignali, C.
DOI
Abstract
We present the X-ray spectral analysis of the 1855 extragalactic sources in the Chandra COSMOS-Legacy survey catalog having more than 30 net counts in the 0.5-7 keV band. A total of 38% of the sources are optically classified type 1 active galactic nuclei (AGNs), 60% are type 2 AGNs, and 2% are passive, low-redshift galaxies. We study the distribution of AGN photon index Γ and of the intrinsic absorption {N}{{H},{{z}}} based on the sources’ optical classification: type 1 AGNs have a slightly steeper mean photon index Γ than type 2 AGNs, which, on the other hand, have average {N}{{H},{{z}}} ∼ 3 times higher than type 1 AGNs. We find that ∼15% of type 1 AGNs have {N}{{H},{{z}}}\gt {10}22 cm-2, I.e., are obscured according to the X-ray spectral fitting; the vast majority of these sources have {L}2{--10{keV}} \gt 1044 erg s-1. The existence of these objects suggests that optical and X-ray obscuration can be caused by different phenomena, the X-ray obscuration being, for example, caused by dust-free material surrounding the inner part of the nuclei. Approximately 18% of type 2 AGNs have {N}{{H},{{z}}}\lt {10}22 cm-2, and most of these sources have low X-ray luminosities (L {}2{--10{keV}} \lt 1043 erg s-1). We expect a part of these sources to be low-accretion, unobscured AGNs lacking broad emission lines. Finally, we also find a direct proportional trend between {N}{{H},{{z}}} and host-galaxy mass and star formation rate, although part of this trend is due to a redshift selection effect.
Volume
830
Issue
2
Start page
100
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2016ApJ...830..100M
Rights
open.access
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