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. KarimC. Laigle, S. M. Lamassa, K. Jahnke, P. Ranalli, K. Schawinski, E. Schinnerer, J. D. Silverman, V. Smolcic, H. Suh, B. Trakhtenbrot

Research output: Contribution to journalArticlepeer-review


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 deg2 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 μm 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 μm 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 toward 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 AGNs and the hard band luminosity, finding a different behavior between the optically and X-ray classified obscured fraction.

Original languageEnglish
Article number34
JournalAstrophysical Journal
Issue number1
StatePublished - 20 Jan 2016
Externally publishedYes


  • X-rays: general
  • catalogs
  • cosmology: observations
  • galaxies: active
  • galaxies: evolution
  • surveys

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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