Spectral index studies of extragalactic radio sources

Spectral index distributions can be indicated conveniently by gsub(S)sup(γ1)(αsub(γ1,γ2)), i.e. the distribution of the two-point spectral index between frequencies γ1 and γ2 for a sample of radio sources complete to flux density S at the selection frequency γ1 (flux densities are expressed in Jy and frequencies in GHz). Such a detailed specification is necessary because g(α) has been found to depend on all three parameters. The author describes recent spectral index information for weak sources selected at 1.4 GHz as well as work on spectral index/optical identification correlations in 5 GHz samples. (Auth.)