A deep ROSAT survey - VIII. X-ray detection of the evolved galaxy cluster 0055-279
Abstract
On a deep (49-ks) ROSAT pointing near the South Galactic Pole, we detect an extended X-ray source, with hard X-ray colours, at a position corresponding to the 0055-279 galaxy cluster. Previous optical investigations indicated that this cluster is at a high redshift of z=0.561 and possesses a much higher fraction of blue spiral galaxies than do local rich clusters. The observed X-ray luminosity of L_X(0.5-2.0 keV)~=10^44 erg s^-1 is only slightly lower than the L_X(0.5-2.0 keV)~=1.5x10^44 erg s^-1 luminosity expected for a local cluster of the same richness. Our results therefore support recent findings that Butcher-Oemler clusters, observed at earlier stages of evolution when they still contain blue spiral galaxies, produce high X-ray luminosities similar to those of present-day rich clusters. We also find that the spectral energy distribution of the 0055-279 cluster shows evidence of stronger absorption at soft energies than would be expected from Galactic hydrogen, suggesting that there is significant (N_H<~10^20 cm^-2) neutral hydrogen absorption within the cluster itself. This may indicate the presence of a cooling flow. The detection of a high-redshift cluster with the observed flux of 0055-279 in our survey area and the numbers of <e1>z<~</e1>0.5 clusters detected on ROSAT images by Castander et al. are consistent with no evolution of the cluster X-ray luminosity function to z~0.6.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 1995
- DOI:
- 10.1093/mnras/276.3.706
- Bibcode:
- 1995MNRAS.276..706R
- Keywords:
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- SURVEYS;
- GALAXIES: CLUSTERS: INDIVIDUAL: 0055-279;
- COOLING FLOWS;
- GALAXIES: EVOLUTION;
- X-RAYS: GALAXIES