The Chandra COSMOS-Legacy survey: source X-ray spectral properties
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634 (United States)
- INAF—Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- ICREA and Institut de Ciències del Cosmos (ICC), Universitat de Barcelona (IEEC-UB), Martí y Franquès 1, E-08028 Barcelona (Spain)
- Institute for Astronomy, 2680 Woodlawn Drive, University of Hawaii, Honolulu, HI 96822 (United States)
- Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2a, FI-00014 Helsinki (Finland)
- Physics and Astronomy Department, Natural Sciences Division, University of Hawaii at Hilo, 200 W. Kawili St., Hilo, HI 96720 (United States)
- Instituto de Astronomía sede Ensenada, Universidad Nacional Autónoma de México, Km. 103, Carret. Tijunana-Ensenada, Ensenada, BC (Mexico)
- Lund Observatory, P.O. Box 43, SE-22100 Lund (Sweden)
- Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching bei München (Germany)
- Institute for Astronomy, Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich (Switzerland)
- Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, Kashiwa, Chiba 277-8583 (Japan)
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{sub 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{sub H,z} ∼3 times higher than type 1 AGNs. We find that ∼15% of type 1 AGNs have N{sub H,z}>10{sup 22} cm{sup −2}, i.e., are obscured according to the X-ray spectral fitting; the vast majority of these sources have L{sub 2--10keV} > 10{sup 44} erg s{sup −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{sub H,z}<10{sup 22} cm{sup −2}, and most of these sources have low X-ray luminosities (L {sub 2--10keV} < 10{sup 43} erg s{sup −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{sub H,z} and host-galaxy mass and star formation rate, although part of this trend is due to a redshift selection effect.
- OSTI ID:
- 22868574
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 830; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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