Evidence for strong shocks in the ISM of small radio sources

Abstract

Radio jets deposit energy into the interstellar medium of their host galaxies, and while a jet is still confined within the host it is expected to drive shocks through the gas. Broad [OIII] 5007 profiles trace ionized gas that has been disturbed, the [OI]/H-alpha versus [OIII]/H-beta diagram helps distinguish gas photoionized by an AGN from gas excited by shocks, and the high ionization [NeV] 3426 line traces the hard UV continuum of the accretion disk, which shocks only reproduce at very high velocities. We have selected two samples of radio-loud AGN from a cross-match of the VLA Sky Survey with DESI Data Release 1, at 0.15 < z < 0.5 and with [OI] 6300 detected at > 5-sigma: one with projected radio sizes of 10-15 kpc, whose jets are still inside the host, and one with sizes greater than 25 kpc, whose jets have broken out. We fit the [OIII] and [OI] profiles, measure W80, and classify each source on the BPT diagram. The confined sources have broader [OIII] lines, sit systematically closer to the LINER region, and are detected less often in [NeV], and the [NeV] difference is not explained by redshift or dust. The broad components are not systematically blueshifted, so the confined sources are distinguished by line width rather than by outflow velocity. We then discuss how these results indicate that the jets of the confined sources are driving strong shocks through the interstellar medium of their hosts.