  The morphology of quiescent galaxies has been found to be correlated with the
activity of their central super massive black hole. In this work, we use data
from the first data release of the LOFAR Two$-$Metre Sky Survey (LoTSS DR1) and
the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) to select more than 15
000 quiescent galaxies at $z<0.3$ to investigate the connection between
radio-loud active galactic nuclei (RLAGNs) and the morphology of their host
galaxy. Taking advantage of the depth of LoTSS, we find that the fraction of
RLAGNs with $L_{\rm 150\,MHz}>10^{21}\rm\,W\,Hz^{-1}$ at fixed stellar mass,
velocity dispersion, or surface mass density does not depend on the galaxy
projected axis ratio ($q$). However, the high-power ($L_{\rm
150\,MHz}>10^{23}\rm\,W\,Hz^{-1}$) RLAGNs are more likely to be found in
massive, round galaxies, while the low- and intermediate-power ($L_{\rm
150\,MHz}\leq10^{23}\rm\,W\,Hz^{-1}$) RLAGNs have similar distributions of $q$
to non-RLAGN galaxies. We argue that our results support the picture that
high-power RLAGNs are more easily triggered in galaxies with a merger-rich
history, while low-power RLAGNs can be triggered in galaxies growing mainly via
secular processes. Our work also supports the idea that the low-luminosity
RLAGN may be sufficient for maintenance-mode feedback in low-mass quiescent
galaxies with disc-like morphology, which is based on a simple extrapolation
from the observed energy balance between cooling and RLAGN-induced cavities in
massive clusters. We find no significant difference between the $q$
distributions of RLAGNs likely to be found in clusters and those likely not
found in clusters after controlling the radio luminosity and stellar mass of
the two samples, indicating that the environment does not significantly
influence the morphology--RLAGN correlation.
