Fading AGNs in Poststarburst Galaxies

Abstract The role of active galactic nuclei (AGNs) in quenching galaxies and driving the evolution from star forming to quiescence remains a key question galaxy evolution. We present evidence Mapping Nearby Galaxies at APO survey for fading AGN activity 6/93 poststarburst galaxies. These six show extended emission line regions (EELRs) consistent with ionization past activity, analogous “Hanny’s Voorwerp” other systems where [O iii ] λ 5007 is bright enough be visible broadband imaging. Using infrared luminosities IRAS estimate current luminosities, we find that 5/6 have AGNs which faded peak luminosity required ionized EELRs. Given rate observe EELRs, typical EELR visibility timescale, an how often EELRs would visible, duty cycle during phase. timescale between peaks t ∼ 1.1–2.3 × 10 5 yr. this phase, spends only 5.3% time (or ON = 0.6–1.3 4 yr) its luminous rest spent “off” or low-luminosity length may explain why so few been observed despite feedback work.