Gas Conditions around Fading Active Galactic Nuclei.

Green Bean galaxies (GBs) are rare astronomical objects surrounded by luminous, spatially-extended emission line nebulae from doubly ionized oxygen ([OIII]). The strong emission, which leads to green colors in composite Sloan Digital Sky Survey imaging, is hypothesized to be ionization echoes left behind as the central Active Galactic Nuclei (AGN) faded in ionizing output over the past 10,000-100,000 years. GBs are also thought to be local, low redshift (z~0.3) cousins of the Lyα nebulae found at high redshifts (z~3), potentially giving us a window into how the gas outside galaxies evolves over time. Our goal is to investigate how the gas physical conditions of GBs compare to other AGN samples. Using spectra from the Apache Point Observatory 3.5m telescope, we estimate the gas density and temperature within GB nebulae. Contrasting the properties of AGN-powered GBs versus other AGN samples may help us understand what triggered the supermassive black hole at the center of GBs to ramp down in such dramatic fashion.