The Radio Luminosity Functions of cD Galaxies; The Fuelling of Radio Sources

Abstract

cD galaxies are often found to be centered exactly on an extended X-ray source (e.g. Abramopoulos and Ku, 1983; Jones and Forman, 1984 JF) establishing a special class of extended extragalactic X-ray sources associated with cD galaxies. We report on a correlative study of four observational parameters of cD galaxies, viz. the X-ray luminosity (L_x), radio power (P_1.4) absolute visual magnitude (M_v) and richness (R) of the cD cluster or group. cD Since galaxies are the most luminous galaxies in all three wavelength regimes, correlations amongst the observational parameters can be studied best for these systems. A physical process, which might give rise to a correlation is the accretion of hot X-ray emitting gas by the cD from the general cluster reservoir by means of a “radiative cooling flow” (Gunn and Gott, 1972). If only a small part of the accreted gas reaches the nucleus it would be sufficient to power a nuclear radio source. In the two family evolutionary cluster scheme of JF (1984) the special class of X-ray cD galaxies is referred to as XD systems. These XD systems are characterized by a small X-ray core radius, which indicates that the X-ray gas is trapped in the potential well of the galaxies themselves, rather than that of the total clusters.