Abstract
The work of this thesis divides into two main areas, the evolution of the
environments of powerful, high-redshift radio galaxies, and the astrophysics
of low-redshift active galaxies as inferred from optical, near- and far-infrared
observations.
A study of the relationship between the radio and infrared luminosities of a
sample of 60 high-redshift 3C radio galaxies reveals that the two quantities are
correlated for the most powerful (and thus most distant) examples. It is suggested that the most powerful radio galaxies are subject to galaxy cannibalism,
and will tend to lie in rich environments. Imaging of a sample of 26 powerful
radio galaxies (0.15 < z < 0.82) is presented in order to test this hypothesis. It
is found that radio galaxies at z > 0.3 lie in environments as rich as Abell class
0-1 clusters. The environments of these galaxies are four to five times richer
than those at low redshift (z < 0.3). However, it is not possible to establish
unequivocally whether radio luminosity or epoch is the fundamental parameter
determining the richness of environment. About half of the classical-double (FR
II) type sources lie in rich environments.
Deep IR AS observations of 18 3C radio galaxies (0.01 < z < 0.2) are discussed, and the spectral energy distributions of the six detected objects constructed. The two broad-line radio galaxies show a peak at 25 /xm, possibly
associated with a warm (T ~ 180 K) dust component. Most of their luminosity
is radiated in this component. The narrow-line radio galaxies have large farinfrared luminosities, and this component has a much greater luminosity than
either the X -ray or radio components. However, there is no evidence for a 25 μ
peak.
Near-simultaneous optical and infrared spectrophotometry of a sample of
eight optically bright quasars and one broad-line radio galaxy are presented.
Study of their Paα/Hα and Hα/H/ß ratios reveals that they can not be well
modelled by either reddened or unreddened photoionization models. The observed line-ratios of 3C273 are used as reference points, and reddenings are
derived for rest of the sample with respect to this quasar. Three of the quasars
have 1-2 mag. of dust with respect to 3C273, and data at other wavelengths
supports this conclusion. Two further quasars have infrared line-ratios which
suggest that they too are subject to reddening.
