A Complete Sample of Radio Galaxies

Abstract

We report here some preliminary results of a multi-wavelength study of a complete sample of radio galaxies. The sample is comprised of 93 radio sources from the Parkes 11 cm catalog which are identified with galaxies of 17th magnitude or brighter in the declination zone -17 to -40 . Our objective is to cross-correlate the radio, infrared, optical, and other properties of a properly defined sample of radio galaxies.By going to relatively low flux densities and using an optical mag nitude limit we are approximating a volume-limited sample and consequently have a class of objects which are more representative of radio galaxies as a whole than the 3C sample. Since the 3C radio galaxies are generally of high luminosity, many are also very distant and therefore difficult to study optically. Another common difficulty in the study of radio galaxies is that radio astronomers usually only have access to the heterogeneous optical data which happen to be published on the relevant galaxies and vice-versa. It is the objective of the present work to obtain uniform and comprehensive data at radio, infrared, and optical wavelengths of a com plete sample of relatively nearby radio galaxies.We have mapped all the galaxies in the sample using the VLA, with supplementary data for the larger sources from Molonglo, Fleurs, and Parkes. Near-infrared photometry is being done using the 3.6m telescope at La Silla, and UKIRT. Spectrophotometry of all the radio galaxies and many of their companions has been completed using telescopes at La Silla and Las Campanas, and the AAT. In addition we have UV and X-ray data for several of the galaxies. This sample contains a smaller fraction of classical double radio sources than the 3C sample; these galaxies exhibit more distorted radio structures and are of lower radio and optical luminosity. 90% of them are within z = 0.1. Radio cores, mostly of the flat-spectrum type, have been detected in 80% of the galaxies. Only 6% have obvious radio jets, although there may be some indication of possible jet structure in as many as a third of them. Half of these radio galaxies are smaller than 75 kpc, as

Non-equilibrium populations of hydrogen in high-redshift galaxies

“…The major effects of stimulated emission in radio recombination lines can be demonstrated with the simple model of a steady-state, homogeneous, plane-parallel ionized medium of finite optical thickness (hereafter "the cloud"). The solution of the radiative transfer equation for such a cloud can be given the following useful form (Shaver 1978):…”

“…(2) Low opacities, strong continuum background (Shaver 1978). The background continuum stimulates line transitions in this case, reducing equation (5.1) to ∆SL ≈ −τLS0 .…”