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The Chandra COSMOS Survey: III. Optical and Infrared Identification of X-ray Point Sources | | F. Civano
; M. Elvis
; M. Brusa
; A. Comastri
; M. Salvato
; G. Zamorani
; T. Aldcroft
; A. Bongiorno
; P. Capak
; N. Cappelluti
; M. Cisternas
; F. Fiore
; A. Fruscione
; H. Hao
; J. Kartaltepe
; A. Koekemoer
; R. Gilli
; C. D. Impey
; G. Lanzuisi
; E. Lusso
; V. Mainieri
; T. Miyaji
; S. Lilly
; D. Masters
; S. Puccetti
; K. Schawinski
; N. Z. Scoville
; J. Silverman
; J. Trump
; M. Urry
; C. Vignali
; N. J. Wright
; | | Date: |
22 May 2012 | | Abstract: | The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that
has imaged the central 0.9 deg^2 of the COSMOS field down to limiting depths of
1.9 10^-16 erg cm^-2 s-1 in the 0.5-2 keV band, 7.3 10^-16 erg cm^-2 s^-1 in
the 2-10 keV band, and 5.7 10^-16 erg cm^-2 s-1 in the 0.5-10 keV band. In this
paper we report the i, K and 3.6micron 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 2 sources are truly empty fields.
Making use of the large number of X-ray sources, we update the "classic locus"
of AGN and define a new locus containing 90% of the AGN in the survey with full
band luminosity >10^42 erg/s. We present the linear fit between the total i
band magnitude and the X-ray flux in the soft and hard band, drawn over 2
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 C
and X/O, computed in the hard band, and that 90% of the obscured AGN 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 BH growth at X-ray luminosities of 10^43- 10^44.5
erg/s. | | Source: | arXiv, 1205.5030 | | Services: | Forum | Review | PDF | Favorites | |
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