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arXiv · 1512.01105

The Chandra COSMOS Legacy survey: optical/IR identifications

S. Marchesi·F. Civano·M. Elvis·M. Salvato·M. Brusa·A. Comastri·R. Gilli·G. Hasinger·G. Lanzuisi·T. Miyaji·E. Treister·C. M. Urry·C. Vignali·G. Zamorani·V. Allevato·N. Cappelluti·C. Cardamone·A. Finoguenov·R. E. Griffiths·A. Karim·C. Laigle·S. M. LaMassa·K. Jahnke·P. Ranalli·K. Schawinski·E. Schinnerer·J. D. Silverman·V. Smolcic·H. Suh·B. Trakhtenbrot
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Abstract

We present the catalog of optical and infrared counterparts of the Chandra COSMOS-Legacy Survey, a 4.6 Ms Chandra program on the 2.2 square degrees of the COSMOS field, combination of 56 new overlapping observations obtained in Cycle 14 with the previous C-COSMOS survey. In this Paper we report the i, K, and 3.6 micron identifications of the 2273 X-ray point sources detected in the new Cycle 14 observations. We use the likelihood ratio technique to derive the association of optical/infrared (IR) counterparts for 97% of the X-ray sources. We also update the information for the 1743 sources detected in C-COSMOS, using new K and 3.6 micron information not available when the C-COSMOS analysis was performed. The final catalog contains 4016 X-ray sources, 97% of which have an optical/IR counterpart and a photometric redshift, while 54% of the sources have a spectroscopic redshift. The full catalog, including spectroscopic and photometric redshifts and optical and X-ray properties described here in detail, is available online. We study several X-ray to optical (X/O) properties: with our large statistics we put better constraints on the X/O flux ratio locus, finding a shift towards faint optical magnitudes in both soft and hard X-ray band. We confirm the existence of a correlation between X/O and the the 2-10 keV luminosity for Type 2 sources. We extend to low luminosities the analysis of the correlation between the fraction of obscured AGN and the hard band luminosity, finding a different behavior between the optically and X-ray classified obscured fraction.

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S. Marchesi, F. Civano, M. Elvis, M. Salvato, M. Brusa, A. Comastri, R. Gilli, G. Hasinger, G. Lanzuisi, T. Miyaji, E. Treister, C. M. Urry, C. Vignali, G. Zamorani, V. Allevato, N. Cappelluti, C. Cardamone, A. Finoguenov, R. E. Griffiths, A. Karim, C. Laigle, S. M. LaMassa, K. Jahnke, P. Ranalli, K. Schawinski, E. Schinnerer, J. D. Silverman, V. Smolcic, H. Suh, B. Trakhtenbrot. 2015-12-03. The Chandra COSMOS Legacy survey: optical/IR identifications. https://doi.org/10.3847/0004-637x%2F817%2F1%2F34

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