A curved 150 pc long jet in the double-peaked emission-line AGN KISSR 434

Abstract

Double-peaked emission lines in the narrow- and/or broad-line spectra of active galactic nuclei (AGNs) have been suggested to arise as a result of disky broad/narrow-line regions, jet–medium interaction, or the presence of binary supermassive black holes. We present the results from 1.5 and 4.9 GHz phase-referenced very long baseline interferometry (VLBI) observations of the Seyfert type 2 galaxy KISSR 434, which exhibits double-peaked emission lines in its optical spectrum. We detect a steep-spectrum (α < −1), curved and long (~150 pc) jet in the VLBI images of KISSR 434. The jet curvature could be a result of precession rather than ram pressure bending from a rotating interstellar medium. Precession could in turn arise as a result of a warped accretion disk or the presence of a binary black hole with a separation of 0.015 pc, not accessible to present-day telescopes. An examination of the emission-line ratios with the MAPPINGS III code reveals that AGN photoionization is likely to be responsible for the observed line ratios and not shock ionization due to the jet. A light (with jet-to-ambient medium density ratio of η ~ 0.01) and fast (with speed vj > 0.75c) precessing jet in KISSR 434 may have stirred up the emission-line gas clouds to produce the observed splits in the narrow-line peaks but is not powerful enough to shock-ionize the gas.