Investigating the spectra and physical nature of galaxy scale jets

Abstract

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″ 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.

Accretion mode versus radio morphology in the LOFAR Deep Fields

“…This additional analysis of our smaller source categories also further supports the argument made earlier that the lack of significant difference in the size distribution of HERGs and LERGs in our sample contradicts a scenario in which all FRII sources start their lives as HERGs and then switch to a lower accretion rate once they have exhausted their initial supply of gas. This is also consistent with the small HERG fraction in the LOFAR galaxy-scale jet sample of Webster et al (2021a) and Webster et al (2021b). We note that of course this doesn't rule out a small fraction of the FRII LERGs being older/fading systems, but this scenario cannot explain the population as a whole.…”

The Faraday Rotation Measure Grid of the LOFAR Two-metre Sky Survey: Data Release 2

“…Including upper limits for the unresolved sources to a median linear size for the RM Grid sources of ∼300 kpc, highlighting that the majority of polarized sources at low frequencies are large radio galaxies. There are 284 ( 457 The faintest, and one of the smallest radio galaxies in the sample, is NGC 5322, with L 144MHz ∼ 2.3 × 10 22 W Hz −1 and a linear size of ∼26 kpc, falling into the category of a 'galaxy-scale jet' (Webster et al 2021 ). The detection in polarization of a galaxy-scale jet is somewhat surprising as the influence of Faraday depolarization is expected to be quite strong on small scales within host galaxy halos (e.g.…”

Molecular flows in contemporary active galaxies and the efficacy of radio-mechanical feedback

“…Radio AGN are also found in giant ellipticals in less dense atmospheres capable of driving both HI and molecular flows (Morganti et al 2005). In these systems the radio energy may be a significant fraction of the thermal energy in their atmospheres, indicating that the radio jets are heating the atmospheres and driving away hot gas from their elliptical galaxy hosts (Webster et al 2021b;Morganti et al 2021).…”