Radio properties of spiral galaxies in high-density groups

Abstract

Radio-continuum observations with the Very Large Array (VLA) of 133 spiral galaxies in 68 Hickson Compact Groups are used to investigate possible enhancement of the effects of interactions among galaxies in such high-density groups. In most of the 56 HCG spirals that were detected the radio radiation is confined to slightly extended nuclear regions suggestive of starburst activity. It is found that the total radio radiation from compact group spirals is significantly lower than from a comparison sample of isolated spirals. However, the radio radiation from the nuclear regions is more than 10 times that from comparable regions in the comparison sample. This effect is more dominant in late-type spirals than it is in early-type spirals. The observations are interpreted in a scenario, suggested by numerical simulation studies by a number of authors, in which galaxy interactions are shown to cause both massive inflows of gas towards the centres of galaxies and outflows from the outer regions. The resultant star formation activity at the centre leads to the formation of supernovae and the subsequent radio radiation. On the other hand, the outflow from the outer regions may be expected to remove the gas and magnetic fields from the disc, resulting in reduced disc radio emission. Observations of gaseous and molecular line distributions may be expected to provide kinematic information for modelling of specific interacting systems