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 journalReview article

112 Scopus citations


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 (US)
Article number34
JournalAstrophysical Journal
Issue number1
StatePublished - Jan 20 2016



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

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Marchesi, S., Civano, F., Elvis, M., Salvato, M., Brusa, M., Comastri, A., Gilli, R., Hasinger, G., Lanzuisi, G., Miyaji, T., Treister, E., Urry, C. M., Vignali, C., Zamorani, G., Allevato, V., Cappelluti, N., Cardamone, C., Finoguenov, A., Griffiths, R. E., ... Trakhtenbrot, B. (2016). THE CHANDRA COSMOS LEGACY SURVEY: OPTICAL/IR IDENTIFICATIONS. Astrophysical Journal, 817(1), [34].