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Published March 1, 2016 | Submitted + Published
Journal Article Open

The Chandra COSMOS Legacy survey: overview and point source catalog


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 deg^2 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) erg cm^(-2)s^(-1) 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 >10^(22) 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.

Additional Information

© 2016. The American Astronomical Society. Received 2015 July 31; accepted 2015 December 24; published 2016 February 29. The authors thank the referee for the useful comments. F. C. and M. C. U. gratefully thank Debra Fine for her support to women in science and the Chandra EPO team, in particular J. De Pasquale, for creating the true-color X-ray image. This research has made use of data obtained from the Chandra Data Archive and software provided by the Chandra X-ray Center (CXC) in the CIAO application package. This work was supported in part by NASA Chandra grant number GO7-8136A (F.C., S.M., V.A., M.E., H.S.); PRIN-INAF 2014 "Windy Black Holes combing galaxy evolution" (A.C., M.B., G.L. and C.V.); the FP7 Career Integration Grant "eEASy": "Supermassive blackholes through cosmic time: from current surveys to eROSITA-Euclid Synergies"(CIG 321913; M.B. and G.L.); UNAM-DGAPA Grant PAPIIT IN104113 and CONACyT Grant Científica Básica #179662 (T.M.); Collaborative Research Council 956, sub-project A1, funded by the Deutsche Forschungsgemeinschaft (A.K.); NASA contract NAS8-03060 (T.A., A.F., K.G.); the Greek General Secretariat of Research and Technology in the framework of the Programme of Support of Postdoctoral Researchers (P.R.); NASA award NNX15AE61G (R.G.); the Science and Technology Facilities Council through grant code ST/I001573/1 (D.M.A.); the Swiss National Science Foundation Grant PP00P2_138979/1 (K.S.); the Center of Excellence in Astrophysics and Associated Technologies (PFB 06), by the FONDECYT regular grant 1120061 and by the CONICYT Anillo project ACT1101 (E.T.); the European Union's Seventh Framework Programme under grant agreements 337595 (ERC Starting Grant, "CoSMass") and 333654 (CIG, AGN feedback; V.S.). S.T. is part of The Dark Cosmology Centre, funded by the Danish National Research Foundation. B.T. is a Zwicky Fellow.

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Published - apj_819_1_62.pdf

Submitted - 1601.00941v1.pdf


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August 20, 2023
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