The TELPERION survey for extended emission regions around AGN: a strongly-interacting and merging galaxy sample

Abstract: We present the results of a search for Extended Emission-Line Regions (EELRs) ionized by extant or recently-faded active galactic nuclei (AGN), using [O III] narrowband imaging and spectroscopic followup. The sample includes 198 galaxies in 92 strongly interacting or merging galaxy systems in the range z=0.009-0.0285. Among these, three have EELRs extended beyond 10 kpc in projection from the nucleus detected in previous studies. We identify a single new distant emission region, projected 35 kpc from UGC 5941. Our optical spectrum does not detect He II, but its strong-line ratios put this in the same class as securely characterized EELR clouds. The nucleus of UGC 5941 is dominated by recent star formation, preventing detection of any weak ongoing AGN. Overall counts of distant EELRs in this and the previous TELPERION samples give incidence 2-5% depending on galaxy and AGN selection, 20-50 times higher than the Galaxy Zoo EELR survey with its higher surface-brightness threshold and much larger input sample. AGN in interacting and merging systems have an increased detection rate $12+/-6$%, while none are detected around noninteracting AGN. Some of these AGN are at luminosity low enough to require additional X-ray or far-infrared information to tell whether the EELR ionization level suggests long-term fading.