Double-Peaked Emission Lines due to A Radio Outflow in KISSR1219

TL;DR

This study uses radio and optical observations to show that a Seyfert 2 galaxy's double-peaked emission lines are caused by a radio outflow pushing emission line clouds, rather than a binary black hole system.

Contribution

It provides the first detailed radio and optical analysis linking radio outflows to double-peaked emission lines in KISSR1219, challenging the binary black hole hypothesis.

Findings

Detection of a one-sided core-jet structure indicating an AGN outflow.

Absence of dual parsec-scale radio cores argues against a binary black hole.

Evidence of shock-heated gas and outflow-driven emission line clouds.

Abstract

We present the results from 1.5 and 5 GHz phase-referenced VLBA and 1.5 GHz Karl G. Jansky Very Large Array (VLA) observations of the Seyfert 2 galaxy KISSR1219, which exhibits double peaked emission lines in its optical spectrum. The VLA and VLBA data reveal a one-sided core-jet structure at roughly the same position angles, providing evidence of an AGN outflow. The absence of dual parsec-scale radio cores puts the binary black hole picture in doubt for the case of KISSR1219. The high brightness temperatures of the parsec-scale core and jet components ($>10^6$ K) are consistent with this interpretation. Doppler boosting with jet speeds of $\gtrsim0.55c$ to $\gtrsim0.25c$, going from parsec- to kpc-scales, at a jet inclination $\gtrsim50^\circ$ can explain the jet one-sidedness in this Seyfert 2 galaxy. A blue-shifted broad emission line component in [O {\sc iii}] is also indicative of an outflow in the emission line gas at a velocity of $\sim350$ km s$^{-1}$, while the [O {\sc i}] doublet lines suggest the presence of shock-heated gas. A detailed line ratio study using the MAPPINGS III code further suggests that a shock+precursor model can explain the line ionization data well. Overall, our data suggest that the radio outflow in KISSR1219 is pushing the emission line clouds, both ahead of the jet and in a lateral direction, giving rise to the double peak emission line spectra.