THE CHANDRA COSMOS SURVEY. III. OPTICAL AND INFRARED IDENTIFICATION OF X-RAY POINT SOURCES

Journal Article · Wed Aug 01 00:00:00 EDT 2012 · Astrophysical Journal, Supplement Series

DOI:https://doi.org/10.1088/0067-0049/201/2/30· OSTI ID:22047589

Civano, F; Elvis, M; Aldcroft, T; Fruscione, A; Hao, H; Lanzuisi, G ^[1]; Brusa, M; Salvato, M; Bongiorno, A ^[2]; Comastri, A; Zamorani, G; Cappelluti, N; Gilli, R; Lusso, E ^[3]; Capak, P ^[4]; Cisternas, M ^[5]; Fiore, F ^[6]; Kartaltepe, J ^[7]; Koekemoer, A ^[8]; Impey, C D ^[9] ; others, and

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1. Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
2. Max Planck Institut fuer Extraterrestrische Physik, Giessenbach Strasse 1, D-85748 Garching (Germany)
3. INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy)
4. California Institute of Technology, 1201 East California Boulevard, Pasadena, CA 91125 (United States)
5. Max-Planck-Institut fuer Astronomie, Konigstuhl 17, D-69117 Heidelberg (Germany)
6. INAF-Osservatorio Astronomico di Roma, via Frascati 33, Monteporzio-Catone (Roma) I-00040 (Italy)
7. Institute for Astronomy, 2680 Woodlawn Drive, University of Hawaii, Honolulu, HI 96822 (United States)
8. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
9. Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that has imaged the central 0.9 deg{sup 2} of the COSMOS field down to limiting depths of 1.9 Multiplication-Sign 10{sup -16} erg cm{sup -2} s{sup -1} in the soft (0.5-2 keV) band, 7.3 Multiplication-Sign 10{sup -16} erg cm{sup -2} s{sup -1} in the hard (2-10 keV) band, and 5.7 Multiplication-Sign 10{sup -16} erg cm{sup -2} s{sup -1} in the full (0.5-10 keV) band. In this paper we report the i, K, and 3.6 {mu}m identifications of the 1761 X-ray point sources. We use the likelihood ratio technique to derive the association of optical/infrared counterparts for 97% of the X-ray sources. For most of the remaining 3%, the presence of multiple counterparts or the faintness of the possible counterpart prevented a unique association. For only 10 X-ray sources we were not able to associate a counterpart, mostly due to the presence of a very bright field source close by. Only two sources are truly empty fields. The full catalog, including spectroscopic and photometric redshifts and classification described here in detail, is available online. Making use of the large number of X-ray sources, we update the 'classic locus' of active galactic nuclei (AGNs) defined 20 years ago in soft X-ray surveys and define a new locus containing 90% of the AGNs in the survey with full-band luminosity >10{sup 42} erg s{sup -1}. We present the linear fit between the total i-band magnitude and the X-ray flux in the soft and hard bands, drawn over two orders of magnitude in X-ray flux, obtained using the combined C-COSMOS and XMM-COSMOS samples. We focus on the X-ray to optical flux ratio (X/O) and we test its known correlation with redshift and luminosity, and a recently introduced anti-correlation with the concentration index (C). We find a strong anti-correlation (though the dispersion is of the order of 0.5 dex) between X/O computed in the hard band and C and that 90% of the obscured AGNs in the sample with morphological information live in galaxies with regular morphology (bulgy and disky/spiral), suggesting that secular processes govern a significant fraction of the black hole growth at X-ray luminosities of 10{sup 43}-10{sup 44.5} erg s{sup -1}. We also investigate the degree of obscuration of the sample using the hardness ratio, and we compare the X-ray color with the near-infrared to optical color.

• OSTI ID: 22047589
• Journal Information: Astrophysical Journal, Supplement Series, Vol. 201, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0067-0049
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTROPHYSICS
BLACK HOLES
CATALOGS
COMPARATIVE EVALUATIONS
CORRELATIONS
GALAXY NUCLEI
INFRARED RADIATION
KEV RANGE
LUMINOSITY
MORPHOLOGY
PHOTOMETRY
POINT SOURCES
RED SHIFT
SOFT X RADIATION
UNIVERSE
VISIBLE RADIATION
X-RAY GALAXIES
X-RAY SOURCES
X-RAY SPECTROSCOPY