“Green-bean galaxies”

Add yet another group to the world of galaxies: the “green beans.” These are a rare class of galaxies that appear green because of extremely strong emission from ionized oxygen. Unusually, the emission extends over the entire galaxy, rather than being confined to the center as is typical of quasars. Mischa Schirmer (Gemini Observatory) and collaborators identified one extreme example, called J2240, in images from the Canada-France-Hawaii Telescope (Figure 1). The collective picture that emerges in subsequent observations from Gemini South and the Very Large Telescope of this and other “green-bean galaxies” is that these are remnant “light echoes” of powerful quasars, after the central engines have shut down. Spectroscopic observations of 19 additional candidates with GMOS-S verified their cosmological distances and confirmed a total of 17 galaxies as green beans similar to J2240. The full results will appear in the Astrophysical Journal, with a preprint currently available at http://arxiv.org/abs/1211.7098 and background information from Gemini at http://www.gemini.edu/node/11904.