Quasar Ionization Echoes -- 100,000 Year Baseline AGN Light Curves

Green Bean galaxies (GBs, Schirmer et al. 2013) are extremely rare type-2 AGN. Only 17 were found in the 14,500 square degrees SDSS-DR9, with redshifts in the range 0.19 < z < 0.34. They feature ultra-luminous and large (up to 100 kpc) narrow-line regions (NLRs) with typical [OIII] luminosities of several 1e43 erg/s. Comparing [OIII] and 22micron WISE luminosities with those of other type-2 quasars, we found the GB [OIII] luminosities to be 5-50 times higher than expected from the control sample. This implies that the central supermassive black hole (SMBH) engines in GBs currently undergo a substantial decline, while the NLR is still being ionized by the escaping X-ray radiation. These ionization echoes provide a unique window into what could be the final shut-down process of quasars. In our project we combine high-resolution narrow-band imaging with ACS/HST, IFU spectroscopy with GMOS/Gemini, and X-ray data with Chandra to study the ionization echoes further. Using the spatially resolved NLRs and the finite speed of light, we can reconstruct individual AGN X-ray light curves over a baseline of up to 100,000 years. This is the same time-scale as predicted for the shut-down by accretion models, and has not been probed previously. Combining the AGN's long-term variability with the physical properties of the luminous NLR then allows us to study the formation of the latter, together with AGN feedback and the impact on star formation in these exotic galaxies.