Variations in emission spectrum over southern radio sources of large angular extent

Sixteen extragalactic sources of large angular extent have been observed at 5000 MHz with the Parkes 64-m telescope (FWHP 4 arcmin). The structures are compared with those determined at 408 MHz from the Molonglo Cross telescope (FWHP 3 arcmin), and in several cases spectral variations over the sources are apparent. In a discussion extending the comparison to other sources for which similar observations are available, it is shown that spectral variations occur more frequently (but not exclusively) in the sources with lower luminosity, and that the nature of the variation depends on luminosity. (author)