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GCPTSRCCXO - Chandra Point Sources in 18 Distant Galaxy Clusters

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Overview

With the superb angular resolution of the Chandra Observatory, it is now possible to detect X-ray point sources, either embedded in galaxy clusters or along the cluster line of sight, which could not be resolved by previous instruments. This now allows studies of source counts in distant cluster fields. The authors want to analyze the inner region of clusters of galaxies to check for the presence of any over-density of X-ray point sources embedded in the gas diffuse emission. These point sources are possible AGN belonging to the clusters and could contaminate the cluster emission. The authors used a sample of 18 distant (0.25 < z < 1.01) galaxy clusters from the Chandra archive to construct the log N - log S relation, in both the soft and hard energy bands, for the X-ray point sources detected in the central cluster region to be compared with the counts of point sources detected in similarly deep fields without clusters.

The authors find a ~2-sigma excess of cluster region sources at the bright end of the log N - log S distributon. The radial distribution of the brightest X-ray point sources confirms this excess and indicates that it is confined to the inner 0.5 Mpc of the cluster region. The results suggest the possible existence of X-ray sources belonging to the cluster (most probably AGN, given their 0.5-10 keV luminosity ranging from 1043 to 1044 erg s-1): on average one every three clusters. Unlike previous studies, which have mainly investigated the point-source population in the vicinity of the galaxy clusters, the present study analyzes the content of point sources within the 1 Mpc region covered by the cluster extent. This work confirms the findings of other investigators who analyzed the central 1 Mpc region of more massive clusters and/or groups in a similar redshift range. The X-ray source excess found here is much smaller than the excess of radio galaxies found recently in high-z X-ray selected clusters, possibly due to the better sensitivity of the radio observations.

The properties of the clusters and of the Chandra exposures in which they were observed are given in Table 1 of the reference paper, and are reproduced below:

Cluster Namne       z    RA (J2000) Dec    ObsID ACIS Mode Exp N_H  L_sb L_hb
                         h  m  s   d  '  "                 ks [units are below]

Abell 2125        0.246 15 41 12 +66 16 01 2207   I   VF  79.7 2.77 0.13 0.56
ZW CL 1454.8+2233 0.258 14 57 15 +22 20 33 4192   I   VF  91.4 3.22 0.23 0.74
MS 1008.1-1224    0.302 10 10 32 -12 39 23  926   I   VF  44.2 6.74 0.44 1.57
ZW CL 0024.0+1652 0.394 00 26 35 +17 09 39  929   S   VF  36.7 4.19 0.34 2.22
MS 1621.5+2640    0.426 16 23 36 +26 34 21  546   I   F   30.0 3.59 0.81 3.41
RXJ 1701.3+6414   0.453 17 01 24 +64 14 10  547   I   VF  49.5 2.59 0.64 2.67
CL 1641+4001      0.464 16 41 53 +40 01 46 3575   I   VF  44.0 1.02 0.67 2.62
V 1524.6+0957     0.516 15 24 40 +09 57 48 1664   I   VF  49.9 2.92 0.89 3.29
MS 0451.6-0305    0.539 04 54 12 -03 00 53  902   S   F   41.5 5.18 0.73 4.12
V 1121+2327       0.562 11 20 57 +23 26 27 1660   I   VF  66.9 1.30 0.73 3.00
MS 2053.7-0449    0.583 20 56 21 -04 37 51 1667   I   VF  43.5 4.96 1.32 4.91
V 1221+4918       0.700 12 21 26 +49 18 30 1662   I   VF  79.4 1.44 1.18 4.62
MS 1137.5+6625    0.782 11 40 22 +66 08 18  536   I   VF 117.5 1.18 0.81 4.04
RDCSJ 1317+2911   0.805 13 17 21 +29 11 19 2228   I   VF 111.3 1.04 0.85 3.59
RDCSJ 1350+6007   0.805 13 50 48 +60 06 54 2229   I   VF  58.3 1.76 1.77 7.26
RXJ 1716.4+6708   0.813 17 16 49 +67 08 26  548   I   F   51.5 3.71 2.17 9.45
MS 1054.4-0321    0.830 10 56 59 -03 37 37  512   S   F   67.5 3.67 1.07 6.61
WARPJ 1415.1+3612 1.013 14 15 11 +36 12 00 4163   I   VF  89.2 1.10 1.93 7.54
where Exp is the Chandra exposure time in ks corresponding to the nominal exposure filtered to exclude time periods of high background, N_H is the Galactic hydrogen column density in the direction of the cluster of galaxies, in units of 1020 cm-2, and L_sb and L_hb are the limiting luminosities in units of 1042 erg s-1 for point sources in the clusters in the 0.5-2.0 kev and 2-10 keV energy bands, respectively.

Catalog Bibcode

2007A&A...462..449B

References

Chandra point-source counts in distant galaxy clusters.
    Branchesi M., Gioia I.M., Fanti C., Fanti R., Cappelluti N.
   <Astron. Astrophys., 462, 449-458 (2007)>
   =2007A&A...462..449B

Provenance

This table was created by the HEASARC in September 2010 based on the electronic version of Table 2 from the reference paper which was obtained from the CDS, their catalog J/A+A/462/449.

Parameters

Cluster
The name of the cluster as given by the authors. Notice that these names do not always conform with the names recommended by the Dictionary of Nomenclature of Celestial Objects.

Search_Radius
The search radius for the cluster of galaxies, in arcseconds, being the angular radius that includes the cluster region where diffuse emission is still detectable. It is thus the radius at which the cluster surface brightness profile merges into the backgroun, and beyond which no further significant cluster emission is detectable.

Source_Number
The X-ray point source identification number from WAVDETECT; this is unique within the specified cluster of galaxies.

Name
The X-ray point source designation constructed by combining the prefix '[BGF2007]' (for Brancesi, Gioia, Fanto 2007), the cluster name and the source number. Notice that the cluster names do not always conform with the names recommended by the Dictionary of Nomenclature of Celestial Objects, e.g., the authors use 'Abell' rather than 'ACO' as the prefix for Abell clusters.

Alt_Name
The HEASARC has constructed this alternative name for the X-ray point source using the procedure recommended by the Dictionary of Nomenclature of Celestial Objects for Chandra X-ray sources, e.g., the CXOU prefix for 'Chandra X-ray Observatory, unregistered' and the J2000.0 equatorial coordinates, truncated to 0.1 seconds of time in RA and 1 arcsecond in Dec.

RA
The Right Ascension of the X-ray point source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 seconds of time in the original table.

Dec
The Declination of the X-ray point source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 arcseconds in the original table.

LII
The Galactic Longitude of the X-ray point source.

BII
The Galactic Latitude of the X-ray point source.

SB_Counts
The net counts in the 0.5-2.0 keV soft energy band for the X-ray point source.

SB_Source_Flag
This flag parameter is set to 'N' to indicates a 'non-used source'. Such sources were not used in Section 5 of the reference paper for the computation of the source counts in the soft band, since their flux is smaller than the flux corresponding to 20% of the sky coverage (see Appendix C of the reference paper for more details).

HB1_Counts
The net counts in the 2.0-7.0 keV energy band for the X-ray point source.

HB1_Source_Flag
This flag parameter is set to 'N' to indicates a 'non-used source'. Such sources were not used in Section 5 of the reference paper for the computation of the source counts in the hard band, since their flux is smaller than the flux corresponding to 20% of the sky coverage (see Appendix C of the reference paper for more details).

SB_Flux
The observed X-ray point source flux in the soft (0.5-2.0 keV) band, in erg s-1 cm-2. This has been calculated as described in Appendix B of the reference paper.

SB_Flux_Error
The RMS uncertainty in the observed X-ray point source flux in the soft (0.5-2.0 keV) band, in erg s-1 cm-2. This has been calculated as described in Appendix B of the reference paper.

SB_Corr_Factor
The correction factor to be applied to the observed soft X-ray flux in order to obtain the Galactic absorption-corrected X-ray flux in this band.

HB_Flux
The observed X-ray point source flux in the hard (2.0-10.0 keV) band, in erg s-1 cm-2. This has been calculated as described in Appendix B of the reference paper. Notice that the hard band used here is different than the 2-7 keV band used for the counts.

HB_Flux_Error
The RMS uncertainty in the observed X-ray point source flux in the hard (2.0-10.0 keV) band, in erg s-1 cm-2. This has been calculated as described in Appendix B of the reference paper.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 27-Sep-2010