Probing gaseous halos of galaxies with radio jets
  Gaseous halos play a key role for understanding inflow, feedback and the
overall baryon budget in galaxies. Literature models predict transitions of the
state of the gaseous halo between cold and hot accretion, winds, fountains and
hydrostatic halos at certain galaxy masses. Since luminosities of radio AGN are
sensitive to halo densities, any significant transition would be expected to
show up in the radio luminosities of large samples of galaxies. The Low
Frequency Array (LOFAR) Two Metre Sky Survey (LoTSS) has indeed identified a
galaxy stellar mass scale, $10^{11} M_\odot$ , above which the radio
luminosities increase disproportionately. Here, we investigate, if radio
luminosities of galaxies, especially the marked rise at galaxy masses around
$10^{11} M_\odot$, can be explained with standard assumptions on jet powers,
scaling between black hole-mass and galaxy mass and gaseous halos. We developed
models for the radio luminosity of radio AGN in halos under infall, galactic
wind and hydrostatic conditions based on observational data and theoretical
constraints, and compared it to LoTSS data for a large sample of galaxies in
the mass rangebetween $10^{8.5} M_\odot$ and $10^{12} M_\odot$. Assuming the
same characteristic upper limit to jet powers as is known from high galaxy
masses to hold at all masses, we find that the maximum radio luminosities for
the hydrostatic gas halos fit well with the upper envelope of the distribution
of the LOFAR data. The marked rise in radio luminosity at $10^{11} M_\odot$ is
matched in our model, and is related to significant change in halo gas density
around this galaxy mass, which is a consequence of the lower cooling rates at
higher virial temperature. Wind and infall models overpredict the radio
luminosities at small galaxy masses and have no particular steepening of the
run of the radio luminosities predicted at any galaxy mass. [...]
