F. Civano, S. Marchesi, A. Comastri, M. C. Urry, M. Elvis, N. Cappelluti, S. Puccetti, M. Brusa, G. Zamorani, G. Hasinger, T. Aldcroft, D. M. Alexander, V. Allevato, H. Brunner, P. Capak, A. Finoguenov, F. Fiore, A. Fruscione, R. Gilli, K. GlotfeltyR. E. Griffiths, H. Hao, F. A. Harrison, K. Jahnke, J. Kartaltepe, A. Karim, S. M. Lamassa, G. Lanzuisi, T. Miyaji, P. Ranalli, M. Salvato, M. Sargent, N. J. Scoville, K. Schawinski, E. Schinnerer, J. Silverman, V. Smolcic, D. Stern, S. Toft, B. Trakhenbrot, E. Treister, C. Vignali

Research output: Contribution to journalArticlepeer-review

264 Scopus citations


The COSMOS-Legacy survey is a 4.6 Ms Chandra program that has imaged 2.2 deg2 of the COSMOS field with an effective exposure of ≃160 ks over the central 1.5 deg2 and of ≃80 ks in the remaining area. The survey is the combination of 56 new observations obtained as an X-ray Visionary Project with the previous C-COSMOS survey. We describe the reduction and analysis of the new observations and the properties of 2273 point sources detected above a spurious probability of 2 × 10-5. We also present the updated properties of the C-COSMOS sources detected in the new data. The whole survey includes 4016 point sources (3814, 2920 and 2440 in the full, soft, and hard band). The limiting depths are 2.2 × 10-16, 1.5 × 10-15, and 8.9 × 10-16 in the 0.5-2, 2-10, and 0.5-10 keV bands, respectively. The observed fraction of obscured active galactic nuclei with a column density >1022 cm-2 from the hardness ratio (HR) is ∼50-16+17%. Given the large sample we compute source number counts in the hard and soft bands, significantly reducing the uncertainties of 5%-10%. For the first time we compute number counts for obscured (HR > -0.2) and unobscured (HR < -0.2) sources and find significant differences between the two populations in the soft band. Due to the unprecedent large exposure, COSMOS-Legacy area is three times larger than surveys at similar depths and its depth is three times fainter than surveys covering similar areas. The area-flux region occupied by COSMOS-Legacy is likely to remain unsurpassed for years to come.

Original languageEnglish (US)
Article number62
JournalAstrophysical Journal
Issue number1
StatePublished - Mar 1 2016
Externally publishedYes


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

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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