Accretion mode versus radio morphology in the LOFAR Deep Fields
  Radio-loud active galaxies have two accretion modes [radiatively inefficient
(RI) and radiatively efficient (RE)], with distinct optical and infrared
signatures, and two jet dynamical behaviours, which in arcsec- to
arcmin-resolution radio surveys manifest primarily as centre- or
edge-brightened structures [Fanaroff-Riley (FR) class I and II]. The nature of
the relationship between accretion mode and radio morphology (FR class) has
been the subject of long debate. We present a comprehensive investigation of
this relationship for a sample of 286 well-resolved radio galaxies in the LOFAR
Two-metre Sky Survey Deep Fields (LoTSS-Deep) first data release, for which
robust morphological and accretion mode classifications have been made. We find
that two-thirds of luminous FRII radio galaxies are RI, and identify no
significant differences in the visual appearance or source dynamic range
(peak/mean surface brightness) of the RI and RE FRIIs, demonstrating that both
RI and RE systems can produce FRII structures. We also find a significant
population of low-luminosity FRIIs (predominantly RI), supporting our earlier
conclusion that FRII radio structures can be produced at all radio
luminosities. We demonstrate that in the luminosity range where both
morphologies are present, the probability of producing FRI or FRII radio
morphology is directly linked to stellar mass, while across all morphologies
and luminosities, RE accretion occurs in systems with high specific star
formation rate, presumably because this traces fuel availability. In summary,
the relationship between accretion mode and radio morphology is very indirect,
with host-galaxy environment controlling these two key parameters in different
ways.
