Investigating the spectra and physical nature of galaxy scale jets
  Previous studies have shown that physically small, low-luminosity radio
galaxies, which we refer to as galaxy scale jets (GSJ), could potentially have
a significant effect upon the host galaxy's evolution. Using 6 arcsec
resolution images taken from the first release of the LOFAR Two Metre Sky
Survey (LoTSS DR1), we identified a representative sample of nine potential GSJ
for which we obtained high-resolution, 2-4 GHz data using the Karl G. Jansky
Very Large Array (VLA). Using these data we aim to verify the GSJ nature of
these sources as well as investigating the potential role of feedback. Our VLA
images reveal a diversity of structures, confirm the hosts for four of the
sources and find that a fifth is the first known example of a galaxy-scale
remnant showing that some radio galaxies never grow beyond the GSJ stage. We
also derive spectral ages and the first estimates of the lobe expansion speeds
of GSJ. We find our GSJ have maximum spectral ages of 60 Myr with most between
about 5 and 20 Myr, consistent with being located along an evolutionary path
joining compact sources and larger radio galaxies. We find lobe advance speeds
a few times the local sound speed, with most GSJ predicted to be driving strong
shocks into their environment and having a significant impact upon the host's
evolution. Our discovery of a remnant GSJ, which will eventually transfer all
of its energy directly into the local environment, represents an important and
previously hidden aspect of AGN life cycles.
