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Up: The spectral index
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In the late seventies not many redshifts of the 4C sample were known. For the
3C sample, redshifts were available for most sources. Therefore only the latter
one was examined by Blumenthal and Miley.
In figure 7 
and 
are plotted against
for (i) the whole 3C sample, (ii) the radio galaxies and
unidentified sources together, and (iii) the quasars. Sources with steeper
spectra tend to have larger redshifts and 178 MHz monochromatic luminosities.
The same result is seen looking at radio galaxies and quasars.