Presentation #341.10 in the session “Galaxy Quenching”.
E+A galaxies represent an important niche of galactic evolution as a subset of post-starburst galaxies whose star formation has been recently and completely quenched. We have analyzed a color-constrained sample of 3,644 galaxies within 3 degrees projected distance from the center of the each of the Hercules clusters (Abell 2147 centered at J160218.76+160111.38, Abell 2151 centered at J160514.88+174454.60, and Abell 2152 centered at J160532.22+162630.04), using data from DR16 of the Sloan Digital Sky Survey. We manually identified 74 “green” and 4 “blue” E+A galaxies and candidates within the cluster using their optical spectra, based on their spectral shape, u-r color, lack of Hα emission, and hydrogen Balmer absorption. Concentrations of these E+As and candidates are found in Abell 2147/2152 and a clump centered around J155736+162400, but are not as prevalent in Abell 2151. One particular object in the sample, Khutulun (2MASX J16015198+1547326), is an example of an E+A SBb-type galaxy, and the inspiration for investigating spiral E+As. Spiral E+As represent an even smaller subgroup of galaxies as they have retained their arms through starburst, and thus were most likely formed without a major galaxy merger. Khutulun appears to support the hypothesis that E+As tend to be in low/medium density regions within clusters, and provides evidence that the gas density distribution is correlated to how quenching is triggered in the galaxies. This work was supported by the Alfred P. Sloan Foundation via the SDSS-IV Faculty and Student Team (FaST) initiative, ARC Agreement SSP483, and by NSF grants AST-1852355, 1852360, 1460939, and 1460860 to the American Museum of Natural History and CUNY College of Staten Island.