Radio Emission in Cooling Flows

Abstract

It is reviewed whether cooling flows could fuel central radio sources in spheroidal galaxies as a general, universal mechanism. The radio luminosity functions of SO, E, gE and cD galaxies show a similar scaled dependence on L _opt , demanding a non-exclusive radio powering mechanism for cD’s. If cooling flows generate the central radio sources in these objects, then a non-exclusive X-ray halo formation process should occur. Gravitational accretion of gas from the inter galactic medium is identified as such a mechanism for both E+SO’s and cD’s. This requires a large mass for the cD’s, to generate a potential well deep enough to bind the gas. Evidence for a large cD mass is discussed. In such a context it is justified to combine the data of several major samples of cD, E and SO galaxies in order to study the relevance of the input scenario. It is found, that for a sample of 111 objects, L _opt is correlated with L _x , log L _opt ~ 0.13logL _x , in a continuous way for the different optical types. The slope of the correlation is consistent with a gravitational accretion scenario. The L _r is strongly correlated with L _x , also in a continuous way over five decades in both luminosities. In the time variable radio source output interpretation , the one-to-one correlation between the integral fraction of radio detections (F(> P) ) and L _x implies a one-to-one correspondence between the peak amplitude of a radio source and the X-ray luminosity of its host galaxy. This is strong evidence for gravitationally driven cooling flows fuelling central radio sources in spheroidal galaxies in general and the results are confirming the input scenario. The cosmological evolution of the scenario is discussed and found to predict L _r ~ (1 + z)⁵.