The Detection of X-Ray Emission from the Highest Redshift Galaxy Clusters
Abstract
We present and analyze deep ROSAT observations of two fields containing the most distant (z > 0.7) optically selected clusters of galaxies currently known. We reliably detect X-ray emission from two clusters (including one at z ~ 0.9) out of five with available redshifts, but we do not detect any emission from a further five candidates without spectroscopic data. Although our distant clusters are expected to be among the richest found optically, their X-ray luminosities (L_x_ ~ 10^44^ h_50_^-2^ ergs s^-1^) are much lower than those of present-day rich clusters. We argue that the clusters we have detected are the only X-ray-luminous examples in the fields surveyed. By considering the likely volume sampled we find evidence for a decline in the comoving number density of clusters to z~1. On the basis of our current small sample, our results are inconsistent with standard hierarchical clustering models in which the gas evolves in a self-similar fashion, indicating that radiative and hydrodynamic processes may be required to account for the low observed luminosities. For example, a cold dark matter model in which the entropy of the intracluster gas is assumed constant predicts a low abundance of luminous clusters at z~0.8 as inferred from our observations.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1994
- DOI:
- 10.1086/187279
- Bibcode:
- 1994ApJ...424L..79C
- Keywords:
-
- Bremsstrahlung;
- Dark Matter;
- Galactic Clusters;
- Galactic Evolution;
- Hydrostatics;
- Sky Surveys (Astronomy);
- X Rays;
- Potential Fields;
- Red Shift;
- Rosat Mission;
- Stellar Luminosity;
- Astrophysics;
- GALAXIES: CLUSTERING;
- GALAXIES: EVOLUTION;
- GALAXIES: LUMINOSITY FUNCTION;
- MASS FUNCTION;
- X-RAYS: GALAXIES;
- X-RAYS: GENERAL