Session 95 - X-Ray Galaxies and Clusters.
Oral session, Wednesday, January 17
La Condesa, Hilton

## [95.01] The X-ray Luminosity Function for Poor Clusters of Galaxies

J. O. Burns, M. Ledlow, C. Loken, A. Klypin (NMSU), W. Voges (MPE), R. A. White (GSFC), G. Bryan, M. Norman (U. Illinois)

We will present the first X-ray Luminosity Function for poor clusters of galaxies. Using a percolation algorithm, White et al. (1996) has compiled a catalog of 600 optically selected groups composed of Zwicky galaxies. This catalog includes MKW and AWM groups (with cD galaxies), many Hickson compact groups, as well as many more loose condensations. We selected a complete,volume-limited subsample of these poor clusters which have at least 4 Zwicky galaxies, b>30\deg, a surface density enhancement of \approx50, and z \le 0.03. We then cross-correlated this sample with the ROSAT all-sky X-ray survey. About 50% of this sample of 50 clusters was detected with 0.5-2.0 keV X-ray luminosities >4 \times 10^41 h_75^-2 ergs/sec. These are the X-ray brightest groups in the northern sky. From this sample, we constructed an X-ray Luminosity Function. We find that this poor cluster luminosity function matches well with that derived for Abell clusters by Briel amp; Henry (1993). It appears that these groups are low mass extensions of rich clusters. We have also derived a mass function for these groups assuming that the X-ray emission is in hydrostatic equilibrium within the clusters. We will compare this mass function with those expected from different cosmological models with different values of Ømega. This research was funded by NSF grant AST93-17596 and NASA grant NAGW-3152.