Observations of a sample of southern radio galaxies

Abstract

The 1415 MHz Fleurs Synthesis Telescope is used to map 25 southern radio galaxies. This significantly extends the sample of southern sources studied with subarcminute resolution and provides a good data base for further study with both large optical telescopes and high resolution radio telescopes. The radio maps are shown overlaid on the optical field and a table is given summarizing the observational results together with estimates of some important parameters for each source. Examples of many types of source morphology are represented in the sample - tails, classical doubles, relaxed doubles, core-halo sources, and cluster emission. Three of the sample sources were observed in greater detail. A radio and optical study of Fornax A (NGC 1316) is described. The dynamics of NGC 1316 are consistent with the galaxy being oblate and flattened by rotation. A radial velocity jump is found at the position of a ripple in the galaxy luminosity profile. This jump is consistent with the formation of shells by the infall of a disk galaxy. Radio observations of Fornax A show a bridge connecting two lobes offset from the parent galaxy. It is shown that this can be explained by the motion of the lobes through a dense intergalactic medium. A spectral index study, together with estimates of the radiative timescales and source lifetimes, shows that energy supply to the relativistic electrons is still occurring even though the energy supply from the galaxy nucleus has apparently switched off. A study is made of the elliptical/spiral pair of galaxies NGC 5090/5091. Associated with the radio source PKS 1318-43 these galaxies show circumstantial evidence that the encounter is affecting the radio source. A spectroscopic and photometric study is undertaken to determine whether mass transfer from the spiral to the elliptical, thus fuelling the central energy source, is dynamically plausible. It is found to be unlikely that the interaction is affecting and/or fuelling the radio source. This is in agreement with previous statistical studies of elliptical galaxies with neighbours. The radio source PKS 0511-48 is found to be identified with a 19th magnitude galaxy. This galaxy contains a long curved filament. A spectroscopic study of the galaxy has found extended emission in the galaxy and filament, with line ratios typical of high ionization narrow line radio galaxies. The filament does not show ordered rotation about the galaxy nucleus. Combined with its morphology, this suggests that it is a tidal arm.