Space Densities for Powerful Radio Sources in the Light of Unification

Abstract

Previous analyses of the space densities of extragalactic radio sources have proceeded on the assumption of two populations: flat-spectrum and steep-spectrum objects, compact and extended in radio structure respectively. It is now generally believed that anisotropic radiation and relativistic beaming effects mean that the steep-spectrum objects are the flat-spectrum objects viewed side-on. The implication is that all previous space density analyses start from the wrong basic premise. There are two unifying paradigms extant for the powerful radio sources, one relating flat-spectrum QSOs and the steep-spectrum FRII sources, the other the BL Lac objects with FRI sources. Our new investigation of space distribution and luminosity functions takes these two populations as a starting point in a new parametric analysis of space densities. The present paper describes the datasets, methodology and first results.