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CCOSMPHOTZ - Chandra COSMOS (C-COSMOS) Survey Photometric Redshift Catalog

HEASARC
Archive

Overview

In their paper, the authors release accurate photometric redshifts for 1692 counterparts to Chandra sources in the central square degree of the Cosmic Evolution Survey (COSMOS) field. The availability of a large training set of spectroscopic redshifts that extends to faint magnitudes enabled photometric redshifts comparable to the highest quality results presently available for normal galaxies. The authors demonstrate that morphologically extended, faint X-ray sources without optical variability are more accurately described by a library of normal galaxies (corrected for emission lines) than by active galactic nucleus (AGN) dominated templates, even if these sources have AGNlike X-ray luminosities. Preselecting the library on the bases of the source properties allowed them to reach an accuracy sigma[Delta-z/(1+Zspec)] ~ 0.015 with a fraction of outliers of 5.8% for the entire Chandra-COSMOS sample. In addition, in this study the authors released revised photometric redshifts for the 1735 optical counterparts of the XMM-detected sources over the entire 2 deg2 of COSMOS (these sources are listed in the HEASARC table XMMCPHOTZ). For 248 sources, their updated photometric redshift differs from the previous release by Delta-z > 0.2. These changes are predominantly due to the inclusion of newly available deep H-band^ photometry (HAB = 24 mag). The authors illustrate once again the importance of a spectroscopic training sample and how an assumption about the nature of a source together, with the number and the depth of the available bands, influences the accuracy of the photometric redshifts determined for AGN. These considerations should be kept in mind when defining the observational strategies of upcoming large surveys targeting AGNs, such as eROSITA at X-ray energies and the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe in the radio band.

This table contains the photometric redshifts and related quantities for 1694 (note that there appears to be 2 more sources than the above-quoted abstract states) Chandra sources in the central square degree of the COSMOS field. Notice that in the original as-published paper no positional information was provided. The HEASARC has assumed that the source numbers used in the present catalog are in the same source numbering scheme as used by Elvis et al. (2009, ApJS, 184, 158, the Chandra COSMOS Survey Point Source Catalog, available at the HEASARC as the CCOSMOSCAT table) and thus obtained the positions and (position-based) names corresponding to these sources.


Catalog Bibcode

2011ApJ...742...61S

References

Dissecting Photometric Redshift for Active Galactic Nucleus Using XMM- and
Chandra-COSMOS Samples
   Salvato M., Ilbert O., Hasinger G., Rau A., Civano F., Zamorani G.,
   Brusa M., Elvis M., Vignali C., Aussel H., Comastri A., Fiore F.,
   Le Floc'h E., Mainieri V., Bardelli S., Bolzonella M., Bongiorno A.,
   Capak P., Caputi K., Cappelluti N., Carollo C. M., Contini T., Garilli B.,
   Iovino A., Fotopoulou S., Fruscione A., Gilli R., Halliday C., Kneib J.-P.,
   Kakazu Y., Kartaltepe J. S., Koekemoer A. M., Kovac K., Ideue Y., Ikeda H.,
   Impey C. D., Le Fevre O., Lamareille F., Lanzuisi G., Le Borgne J.-F.,
   Le Brun V., Lilly S., Maier C., Manohar S., Masters D., McCracken H.,
   Messias H., Mignoli M., Mobasher B., Nagao T., Pello R., Puccetti S.,
   Perez-Montero E., Renzini A., Sargent M., Sanders D. B., Scodeggio M.,
   Scoville N., Shopbell P., Silvermann J., Taniguchi Y., Tasca L., Tresse L.,
   Trump J. R., Zucca E.
  <Astrophys. J., 742, 61 (2011)>
  =2011ApJ...742...61S

Provenance

This table was created by the HEASARC in November 2011 based on an electronic version of Table 4 from the reference paper which was obtained from the ApJ website.

Parameters

Source_Number
A unique identification number for each source in the catalog from Civano et al. (2011, in preparation). The HEASARC has assumed that this is also the source numbering scheme used by Elvis et al. (2009, ApJS, 184, 158, the Chandra COSMOS Survey Point Source Catalog, available at the HEASARC as the CCOSMOSCAT table) in obtaining the positions and (position-based) names corresponding to these sources.

Name
The Chandra source name, following the standard IAU position-based convention, with the prefix "CXOC" for "Chandra X-ray Observatory COSMOS" survey and the J2000.0 source coordinates (taken from the CCOSMOSCAT table).

RA
The Right Ascension of the Chandra source in the selected equinox. This was given in J2000.0 coordinates to a precision of 1 microdegree (3.6 mas) in the CCOSMOSCAT table.

Dec
The Declination of the Chandra source in the selected equinox. This was given in J2000.0 coordinates to a precision of 1 microdegree (3.6 mas) in the CCOSMOSCAT table.

LII
The Galactic Longitude of the Chandra source.

BII
The Galactic Latitude of the Chandra source.

Ilbert_Source_Number
The optical identifier of the source as reported in the optical photometric catalog "cosmos_phot_20081101" available on the COSMOS webpage http://irsa.ipac.caltech.edu/data/COSMOS/tables/photometry/ and/or in the photo-z catalog (Ilbert et al. 2009, ApJ, 690, 1236). A null value for this parameter indicates that the Chandra source has no counterpart in these catalogs.

Phot_Redshift
The photometric redshift of the source. The authors found several dozen candidate stars in this sample of which 18 were already spectroscopically confirmed. A redshift of 0.000 has been assigned in such cases and no information on the PDFz, best fit template, and variability is given.

Phot_Redshift_Min
The lower limit to the value of the photometric redshift. The authors found several dozen candidate stars in this sample of which 18 were already spectroscopically confirmed. A minimum redshift of 0.000 has been assigned in such cases and no information on the PDFz, best fit template, and variability is given.

Phot_Redshift_Max
The upper limit to the value of the photometric redshift. The authors found several dozen candidate stars in this sample of which 18 were already spectroscopically confirmed. A maximum redshift of 0.000 has been assigned in such cases and no information on the PDFz, best fit template, and variability is given.

Redshift_Pdf
The redshift probability distribution function PDFz. No value is provided for objects classified as stars.

Best_Fit_Template
The best-fit template to the spectral energy distribution (SED) using the codes 1-30 as described in Table 2 of Salvato et al. (2009, ApJ, 690, 1250) and adding 100 to the codes 1-31 in the Ilbert et al. (2009, ApJ, 690, 1236) library. No value is provided for objects classified as stars.

Morph_Class
The source morphological classification (Leauthard et al. 2007, ApJS, 172, 219) where values of 1 or 3 indicate extended structure and 2 or 4 indicate point-like sources. Null values represented by -999 in the original table have been replaced by nulls in this HEASARC representation. There are 17 entries which have values of -99; the significance of which the HEASARC is unaware, but which likely should also be null values.

Variability
The variability parameter VAR as defined in equation (1) of Salvato et al. (2009, ApJ, 690, 1250). This describes the deviation of the optical photometry from a reference epoch (2006, the time of quasi-simultaneous optical and Spitzer/IRAC observations). See Section 3 of the reference paper for more details.


Contact Person

Questions regarding the CCOSMPHOTZ database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 22-Nov-2011