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 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 times higher than type 1 AGNs. We find that ∼15% of type 1 AGNs have cm-2, i.e., are obscured according to the X-ray spectral fitting; the vast majority of these sources have 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 cm-2, and most of these sources have low X-ray luminosities (L2-10keV < 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 and host-galaxy mass and star formation rate, although part of this trend is due to a redshift selection effect.

THE CHANDRA COSMOS-LEGACY SURVEY: SOURCE X-RAY SPECTRAL PROPERTIES

LANZUISI, GIORGIO;COMASTRI, ANDREA;ZAMORANI, GIOVANNI;VIGNALI, CRISTIAN
2016

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 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 times higher than type 1 AGNs. We find that ∼15% of type 1 AGNs have cm-2, i.e., are obscured according to the X-ray spectral fitting; the vast majority of these sources have 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 cm-2, and most of these sources have low X-ray luminosities (L2-10keV < 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 and host-galaxy mass and star formation rate, although part of this trend is due to a redshift selection effect.
Marchesi, S.; Lanzuisi, G.; Civano, F.; Iwasawa, K.; Suh, H.; Comastri, A.; Zamorani, G.; Allevato, V.; Griffiths, R.; Miyaji, T.; Ranalli, P.; Salvato, M.; Schawinski, K.; Silverman, J.; Treister, E.; Urry, C.M.; Vignali, C.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/588324
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