Bibcode
Civano, F.; Elvis, M.; Brusa, M.; Comastri, A.; Salvato, M.; Zamorani, G.; Aldcroft, T.; Bongiorno, A.; Capak, P.; Cappelluti, N.; Cisternas, M.; Fiore, F.; Fruscione, A.; Hao, H.; Kartaltepe, J.; Koekemoer, A.; Gilli, R.; Impey, C. D.; Lanzuisi, G.; Lusso, E.; Mainieri, V.; Miyaji, T.; Lilly, S.; Masters, D.; Puccetti, S.; Schawinski, K.; Scoville, N. Z.; Silverman, J.; Trump, J.; Urry, M.; Vignali, C.; Wright, N. J.
Bibliographical reference
The Astrophysical Journal Supplement, Volume 201, Issue 2, article id. 30 (2012).
Advertised on:
8
2012
Citations
210
Refereed citations
203
Description
The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program
that has imaged the central 0.9 deg2 of the COSMOS field down
to limiting depths of 1.9 × 10-16 erg
cm-2 s-1 in the soft (0.5-2 keV) band,
7.3 × 10-16 erg cm-2
s-1 in the hard (2-10 keV) band, and 5.7 ×
10-16 erg cm-2 s-1 in
the full (0.5-10 keV) band. In this paper we report the i, K, and 3.6
μm 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 >1042 erg
s-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
1043-1044.5 erg s-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.
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