© CAMBRIDGE UNIVERSITY PRESS 1999

3. X-RAY PROPERTIES OF GALAXY CLUSTERS

3.1. X-Ray Emission from Clusters

All rich clusters of galaxies produce extended X-ray emission due to thermal bremsstrahlung radiation from a hot intracluster gas (Jones and Forman 1984; Sarazin 1986; David et al. 1993; Edge et al. 1990, 1991; Henry et al. 1991, 1992; Burg et al. 1994). The cluster X-ray luminosity emitted in the photon energy band E₁ to E₂ by thermal bremsstrahlung from a hot (T_x degrees) intracluster gas of uniform electron density n_e and a radius R_x is

(30)

The Gaunt factor correction g (of order unity) is a slowly varying function of temperature and energy. The bolometric thermal bremsstrahlung luminosity of a cluster core can be approximated by

(31)

Some of the main properties of the hot intracluster gas are summarized below.