MERLIN observations of compact sources with very steep radio spectra

MERLIN maps at 408 MHz are presented for six compact very-steep-spectrum radio sources. It is found that all the sources are double, with the flux originating in two compact components, and that the radio properties of the sources differ from those of small-diameter high-luminosity radio galaxies only in their very high spectral indexes. The difference is attributed to a very rapid fading of the energy supply from the central nucleus in a double radio galaxy. It is suggested that the relative scarcity of compact sources with very steep radio spectra could be explained by the short life-time of the steep-spectrum phase (100,000 yr) as compared with the typical source lifetime (at least 1 million yr).