Two Epochs of VLBI Observations of 8 KISSR Seyfert & LINER Galaxies: Suggestions of Fast and Filamentary Outflows

TL;DR

Problem: The origin of double-peaked emission lines in DPAGN and the nature of radio outflows in radio-quiet AGN are not well understood. Approach: The authors present a second epoch of phase-referenced VLBA observations of 8 KISSR DPAGN to trace parsec-scale jets, complemented by 1.5 GHz VLA imaging for four sources. Findings: Parscale radio emission is detected in 7/8 sources; jet-like structures persist over ~4–9 years; tentative superluminal motions are seen in KISSR102 and KISSR872; VLA maps reveal core–lobe/core–halo morphologies; alignment with kpc-scale spectral gradients and SFR discrepancies point to AGN-jet origins and jet expansion to ~200 pc–1 kpc. Conclusions: The KISSR jets exhibit properties akin to those of radio-loud AGN jets despite lower compactness, implying that radio-quiet AGN can host relativistic, evolving jets and that DPAGN double-peaks may arise from multiple mechanisms.

Abstract

We present here the results from a second epoch of phase-referenced VLBA observations of 8 Seyfert and LINER galaxies from the KISSR sample. These sources were chosen based on the presence of double peaks or asymmetries in their emission lines as observed in SDSS spectra. Parsec-scale radio emission is detected in 7 of the 8 sources in the second epoch. Jet-like features appear to persist over a $\sim4-9$ year timeline in these `radio-quiet' AGN. A few sources like KISSR1494, however, show significantly different structures after a 9 year interval. KISSR102, which was previously suggested to be a binary black hole candidate based on the presence of two compact cores, shows the tentative signatures of superluminal jet motion ($1.05\pm0.45$c). Tentative superluminal motion in a jet knot has been reported in another source, KISSR872 ($1.65\pm0.57$c). We present 1.5 GHz images from the VLA A-array of 4 sources. These images reveal core-lobe or core-halo structures. The alignment of the VLBI jet direction with the kpc-scale spectral index gradient, as well as the mismatch between the star formation rate derived from the radio and H$α$ line emission, support the suggestion that the kpc-scale emission is AGN-jet-related. The jets in KISSR sources appear to lose collimation over spatial scales between 200 parsec and 1 kpc. Overall, the characteristics of the KISSR jets are reminiscent of similar properties observed in VLBI monitoring studies of `radio-loud' AGN jets even as subtle differences related to the compactness and brightness of jet features remain.