The nuclear properties and extended morphologies of powerful radio
  galaxies: the roles of host galaxy and environment
  Powerful radio galaxies exist as either compact or extended sources, with the
extended sources traditionally classified by their radio morphologies as
Fanaroff--Riley (FR) type I and II sources. FRI/II and compact radio galaxies
have also been classified by their optical spectra into two different types:
high excitation (HERG; quasar-mode) and low excitation (LERG; jet-mode). We
present a catalogue of visual morphologies for a complete sample of $>$1000
1.4-GHz-selected extended radio sources from the Sloan Digital Sky Survey. We
study the environment and host galaxy properties of FRI/II and compact sources,
classified into HERG/LERG types, in order to separate and distinguish the
factors that drive the radio morphological variations from those responsible
for the spectral properties. Comparing FRI LERGs with FRII LERGs at fixed
stellar mass and radio luminosity, we show that FRIs typically reside in richer
environments and are hosted by smaller galaxies with higher mass surface
density; this is consistent with extrinsic effects of jet disruption driving
the FR dichotomy. Using matched samples of HERGs and LERGs, we show that HERG
host galaxies are more frequently star-forming, with more evidence for
disk-like structure than LERGs, in accordance with currently-favoured models of
fundamentally different fuelling mechanisms. Comparing FRI/II LERGs with
compact LERGs, we find the primary difference is that compact objects typically
harbour less massive black holes. This suggests that lower-mass black holes may
be less efficient at launching stable radio jets, or do so for shorter times.
Finally, we investigate rarer sub-classes: wide-angle tail, head-tail,
FR-hybrid and double-double sources.
