Past AGN Activity in a Post-Starburst Galaxy

Recent studies of post-starburst galaxies (PSBs)—or galaxies that have had a recent burst in star-formation and have since become quiescent—unveil a discrepancy in our understanding of galaxy evolution. Observations of PSBs have revealed molecular gas in quantities similar to that in star-forming galaxies, despite star-formation rates consistent with early-type galaxies. Therefore, “quenching” mechanisms which suppress star formation must act during the ~Gyr long PSB phase. We explore outflows driven by an extremely luminous central super-massive blackhole, or an active galactic nucleus (AGN), as a possible quenching mechanism in the post-starburst galaxy, PGC 043234. Combining 3-dimensional MUSE (Multi-Unit Spectroscopic Explorer, 0.465-0.93 micrometres) integral-field unit cube data with the penalized-pixel galactic and stellar spectrum fitting software (pPXF), we obtain gas emission line flux and reddening values throughout the galaxy. We analyze the bolometric luminosity of the AGN, derived from the flux in Hα at a given radius. PGC 043234 is accompanied by an extended emission line region (EELR, also known as a voorwerp) which spans a range of 2 to 6 kpc from the galaxy nucleus. The EELR therefore allows for a larger radial map of AGN luminosity. Due to the short time scales on which we can measure AGN variability (~10⁴ yrs), such radial maps reveal a luminosity output history of the AGN within the time scale required for rapid quenching. We determine that the emission of the nucleus is currently weak or LINER like, which is consistent with our Baldwin-Philips-Terlevich spatial analysis. Emission signatures at larger radii reveal intense AGN activity, potentially associated with large outflows. The large variability in AGN luminosity observed for this post-starburst galaxy has implications for the role of AGN feedback during this phase and the effects of past AGN activity in galaxies with currently quiescent nuclei.