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CCOSRSSFAG - Chandra COSMOS Radio-Selected Star-Forming Galaxies and AGN Catalog

HEASARC
Archive

Overview

X-ray surveys contain sizable numbers of star-forming galaxies, beyond the AGN which usually make up the majority of detections. Many methods to separate the two populations are used in the literature, based on X-ray and multi-wavelength properties. The authors aim at a detailed test of the classification schemes and to study the X-ray properties of the resulting samples. They build on a sample of galaxies selected at 1.4 GHz in the VLA-COSMOS survey, classified by Smolcic et al. (2008, ApJS, 177, 14) according to their optical colors and also observed by Chandra. A similarly selected control sample of AGN is also used for comparison. The authors review some X-ray based classification criteria and check how they affect the sample composition. The efficiency of the classification scheme devised by Smolcic et al. (2008) is such that ~30% of composite/misclassified objects are expected because of the higher X-ray brightness of AGN with respect to galaxies. The latter fraction is actually 50% in the X-ray detected sources, while it is expected to be much lower among X-ray undetected sources. Indeed, the analysis of the stacked spectrum of undetected sources shows, consistently, strongly different properties between the AGN and galaxy samples. X-ray based selection criteria are then used to refine both samples. The radio/X-ray luminosity correlation for star-forming (SF) galaxies is found to hold with the same X-ray/radio ratio valid for nearby galaxies. Some evolution of the ratio may be possible for sources at high redshift or high luminosity, though it is likely explained by a bias arising from the radio selection. Finally, in their paper the authors discuss the X-ray number counts of star-forming galaxies from the VLA- and C-COSMOS surveys according to different selection criteria, and compare them to the similar determination from the Chandra Deep Fields. The classification scheme proposed here may find application in future works and surveys.

This table contains the catalogs of radio-selected SF- and AGN-candidate sources with an X-ray detection in C-COSMOS which were contained in Tables 2 and 3 of the reference paper, respectively. The HEASARC has merged these into a single table, adding a new parameter sample which is set to 'SFG' for radio-selected SF-candidate sources from Table 2 and to 'AGN' for the AGN-candidate sources from Table 3.


Catalog Bibcode

2012A&A...542A..16R

References

X-ray properties of radio-selected star forming galaxies in the
Chandra-COSMOS survey.
    Ranalli P., Comastri A., Zamorani G., Cappelluti N., Civano F.,
    Georgantopoulos I., Gilli R., Schinnerer E., Smolcic V., Vignali C.
    <Astron. Astrophys. 542, A16 (2012)>
    =2012A&A...542A..16R        (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in June 2012 based on CDS table J/A+A/542/A16 files table2.dat and table3.dat.

Parameters

Name
The J2000.0 position-based VLA-COSMOS source designation as recommended by the Dictionary of Nomenclature of Celestial Objects, i.e., 'COSMOSVLA JHHMMSS.ss+DDMMSS.s'.

RA
The Right Ascension of the source based on its VLA-COSMOS designation in the selected equinox. The latter was given in J2000.0 coordinates to a precision of 0.01 seconds of time.

Dec
The Declination of the source based on its VLA-COSMOS designation in the selected equinox. The latter was given in J2000.0 coordinates to a precision of 0.1 arcseconds.

LII
The Galactic Longitude of the source based on its VLA-COSMOS designation.

BII
The Galactic Latitude of the source based on its VLA-COSMOS designation.

CXO_Name
The J2000.0 position-based Chandra-COSMOS (C-COSMOS) source designation as recommended by the Dictionary of Nomenclature of Celestial Objects, i.e., 'CXOC JHHMMSS.s+DDMMSS'.

CXO_Source_Number
The Chandra X-ray source number from Elvis et al. (2009, ApJS, 184, 158).

Sample
The HEASARC added this new distinguishing parameter, which is set to 'SFG' for radio-selected SF-candidate sources from Table 2 of the reference paper and to 'AGN' for the AGN-candidate sources from Table 3.

Redshift
The spectroscopic redshift of the source, except if redshift_flag is set to 'a' in which cases it is the photometric redshift.

Redshift_Flag
This flag parameter is set to 'a' to indicate that the redshift quoted is photometric rather than spectroscopic.

SB_Flux_Limit
This parameter is set to '<' if the corresponding parameter value is an upper limit rather than a detection.

SB_Flux
The Chandra X-ray flux of the source in the soft band (0.5 - 2 keV), in erg s-1 cm-2. The fluxes of candidate SF galaxies have been recomputed from the counts by assuming a power-law spectrum with a spectral index Gamma of 2.1 instead of the 1.4 value used in Elvis et al. (2009, ApJS, 184, 158). Conversely for the AGN candidates, the authors used the latter harder spectral index of 1.4.

HB_Flux_Limit
This parameter is set to '<' if the corresponding parameter value is an upper limit rather than a detection.

HB_Flux
The Chandra X-ray flux of the source in the hard band (2 - 10 keV), in erg s-1 cm-2. The fluxes of candidate SF galaxies have been recomputed from the counts by assuming a power-law spectrum with a spectral index Gamma of 2.1 instead of the 1.4 value used in Elvis et al. (2009, ApJS, 184, 158). Conversely for the AGN candidates, the authors used the latter harder spectral index of 1.4.

SB_Lx_Limit
This parameter is set to '<' if the corresponding parameter value is an upper limit rather than a detection.

SB_Lx
The rest-frame X-ray luminosity of the source in the soft band (0.5 - 2 keV), in erg s-1.

HB_Lx_Limit
This parameter is set to '<' if the corresponding parameter value is an upper limit rather than a detection.

HB_Lx
The rest-frame X-ray luminosity of the source in the hard band (2 - 10 keV), in erg s-1.

Hardness_Ratio
The Chandra X-ray hardness ratio HR = (H-S)/(H+S), where H and S are the net (i.e., background-subtracted) counts in the hard and soft bands, respectively.

Xray_Opt_Ratio_Limit
This parameter is set to '<' if the corresponding parameter value is an upper limit.

Xray_Opt_Ratio
The X-ray/optical flux ratio X/O defined by X/O = log (FX) + 0.4R + 5.71, where FX is the 0.5-2.0 keV soft-band flux and R is the R-band optical apparent magnitude. See Section 4.2 of the reference paper for more details about this flux ratio and its use as a classifier.

Xray_Radio_Ratio_Limit
This parameter is set to '<' if the corresponding parameter value is an upper limit.

Xray_Radio_Ratio
The logarithmic ratio q of the X-ray flux F_X in the soft band to the radio flux density at 1.4 GHz, S1.4GHz, i.e., q = log (FX/S1.4GHz), in (log) Hz. See Section 7 of the reference paper for more details about this flux ratio.

Source_Type
The optical classification of the source using the following abbreviations:

             T1 = type-1 AGN
             T2 = type-2 AGN
              E = emission line galaxy
              A = absorption line galaxies
              L = low signal/noise spectrum
        (blank) = no spectral information
  

SFG_AGN_Class
The final classification of the source by the authors, viz., whether it is more or less likely to be an SF galaxy than an AGN. In Section 4.5 of the reference paper, the authors discuss a schema for classifying sources in which the X-ray luminosity is produced by star formation rather than an AGN. They list therein 4 conditions indicative of an SF origin of the X-ray luminosity and have divided the studied sources into 3 SF classes with the following meanings:

        1 = source fulfills all the conditions
        2 = source fulfills all conditions but one
        3 = source for which there are at least two conditions not satisfied
  
Thus, class 1 comprises a conservative sample of SF galaxies, 1 and 2 comprise a less conservative sample of SF galaxies, and class 3 objects likely do not have the bulk of their X-ray emission powered by star-formation related processes. There are 8 class-1 objects, 8 class-2 objects and 17 class-3 objects in the SFG sample whereas there are 14 class-1 objects, 6 class-2 objects and 62 class-3 objects in the AGN sample.

Class
The HEASARC Browse object classification, based on the source_type value, i.e., the optical classification. The final class derived from the sfg_agn_class value may well differ from this class, notice.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 14-Jun-2012