The Oxygen Content of Blue Elliptical Galaxies

Abstract

A clear bimodal distribution appears when looking at the colors of galaxies. This distribution can be separated into two sequences: one that resides in the blue end of the spectrum and one that resides in the red end of the spectrum. The blue sequence indicates active star formation and is typically populated by spiral galaxies. In contrast, the red sequence lacks star formation and is populated by elliptical galaxies. However, there exist a number of elliptical galaxies that reside in the blue sequence. Using galaxy spectra from the Sloan Digital Sky Survey, I investigated the properties and origins of two samples of blue elliptical galaxies. One sample included 204 high-mass galaxies. The other sample included seventeen low-mass galaxies. Emission-line diagnostics were used to investigate the luminosity-metallicity and mass-metallicity relationships. Both samples were found to lie predominantly above the median trend in luminosity-metallicity space. Masses were available for only one sample, which also appears to lie above the median in mass-metallicity space. Possible causes for these higher metallicities include inflows of gas from the intergalactic medium and mergers with smaller, star-forming galaxies.