The TELPERION Survey for Distant [O III] Clouds around Luminous and Hibernating AGN

TL;DR

This survey identifies distant ionized clouds around AGN, revealing their connection to tidal features and evidence of AGN fading over tens of thousands of years, with implications for understanding AGN activity and galaxy interactions.

Contribution

The paper presents the first deep narrowband [O III] survey of a large sample of AGN hosts, discovering new distant ionized clouds and linking them to tidal debris and AGN variability.

Findings

Discovered two new distant AGN-ionized clouds at 26 and 75 kpc.

Found that ~10% of galaxies with tidal tails host distant EELRs.

Evidence suggests AGN in NGC 5514 faded by over 3 times in 250,000 years.

Abstract

We present a narrowband [O III] imaging survey of 111 AGN hosts and 17 merging-galaxy systems, in search of distant extended emission-line regions (EELRs) around AGN (either extant or faded). Our data reach deeper than detection from the broadband SDSS data, and cover a wider field than some early emission-line surveys used to study extended structure around AGN. Spectroscopic followup confirms two new distant AGN-ionized clouds, in the merging systems NGC 235 and NGC 5514, projected at 26 and 75 kpc from the nuclei (respectively). We also recover the previously-known region in NGC 7252. These results strengthen the connection between EELRs and tidal features; kinematically quiescent distant EELRs are virtually always photoionized tidal debris. We see them in ~10% of the galaxies in our sample with tidal tails. Energy budgets suggest that the AGN in NGC 5514 has faded by >3 times during the extra light-travel time ~250,000 years from the nucleus to the cloud and then to the observer; strong shock emission in outflows masks the optical signature of the AGN. For NGC 235 our data are consistent with but do not unequivocally require variation over ~85,000 years. In addition to these very distant ionized clouds, luminous and extensive line emission within four galaxies - IC 1481, ESO 362-G08, NGC 5514, and NGC 7679. IC 1481 shows apparent ionization cones, a rare combination with its LINER AGN spectrum. In NGC 5514, we measure a 7-kpc shell expanding at ~370 km/s west of the nucleus.