Extragalactic sources with very asymmetric radio structure: VLA and Merlin observations

As part of the study to understand the nature of extragalactic radio sources which are very asymmetric in the surface brightness of the two lobes, often with radio emission on only one side of the nucleus, it is observed that a large number of them have high angular resolution and good surface brightness sensitivity at radio frequencies. In this paper, VLA and MERLIN observations of 15 such sources are presented. Their observed structures and spectra, and possible explanations for their morphologies are discussed. Evidence of a possible correlation between the hot-spot brightness ratio and the degree of core prominence, used as a statistical measure of source orientation is reported suggesting that relativistic beaming of the hot-spot emission does play a significant role in the observed brightness asymmetry. To explain the apparently one-sided sources within the relativistic beaming framework, the velocities required are in the range of 0.2 to 0.8 c. The possibility that the lobe which is seen to the south of the jet in 3C273 is the counter-lobe seen in projection is discussed. Attention to a number of one-sided sources with very weak cores is drawn and their possible nature is discussed. (author). 94 refs., 16 figs., 5 tabs