Peculiar radio structure in the quasar 3C380

Abstract

The majority of powerful extragalactic radio sources have steep radio spectra and angular sizes >5 arc s. Their basically symmetrical double structures can be explained by means of two, originally antiparallel, beams which emanate from a massive object or central engine (CE) and transport energy to the ‘outer lobes’ some 105–106 pc away1. Around one-third of sources, however, are more compact. The flat-spectrum compact sources may be part of the same parent population as the steep-spectrum extended sources but observed end-on rather than broadside-on2,3. As yet, however, we have little understanding of the steep-spectrum compact sources (SSCSs) which have recently been shown to comprise ∼30% of all steep-spectrum objects4,5. We now present radio maps which hint at an explanation for the small size of at least some of these SSCSs. Our maps, of the quasar 3C380, reveal a peculiar radio structure which is difficult to interpret other than by a powerful interaction between the radio-emitting plasma and its environment. Thus, the sub-galactic (projected) dimensions of this and other SSCSs may be a result of the beams being disrupted before they have propagated beyond the parent object.