Probing gaseous halos of galaxies with radio jets

Abstract

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. [...]