The X-Ray Luminosity Function and Gas Mass Function for Optically Selected Poor and Rich Clusters of Galaxies

Abstract

We present the first X-ray luminosity function (XLF) for an optically selected sample of 49 nearby poor clusters of galaxies and a sample of 67 Abell clusters with z ≤ 0.15. We have extended the measured cluster XLF by more than a factor of 10 in X-ray luminosity. Our poor cluster sample was drawn from an optical catalog of groups with 0.01 ≤ z ≤ 0.03 composed of Zwicky galaxies. The X-ray emission was measured from the ROSAT all-sky survey. About 45% of the poor clusters were detected, with 0.5-2.0 keV luminosities from 1.7 to 65 × 1041 h-2 ergs s-1. These are among the X-ray brightest, optically selected poor clusters in the northern hemisphere. For this sample, the poor cluster XLF was found to be a smooth extrapolation of the rich cluster XLF. A new Hydro/N-body simulation of a hot + cold dark matter model with Ωtotal = 1, Ων = 0.2, and a baryon fraction of 7.5% was used to model and understand our observational selection effects. We found that the observed cluster gas mass function was consistent with our model.