Measuring the redshift evolution of Abell clusters and the density variation of the spiral to elliptical galaxy ratio in the Sloan Digital Sky Survey

Abstract

From color photometry (Gunn ugr filter bands) of galaxies found in the Sloan Digital Sky Survey (SDSS) DR6 catalog, I have constructed color-color diagrams for 11 Abell galaxy clusters ranging in redshift from z=.018 to .375. I have classified the galaxies in them as spirals and ellipticals using a technique based on the empirically determined ugr color-color diagrams of known spirals and elliptical. Since star formation has essentially stopped in gas-poor elliptical galaxies, they have fewer younger blue stars (and more older red stars) than spiral galaxies, permitting a segregation of the two galaxies by color. I have measured the number of spiral and elliptical galaxies in each cluster and examine the behavior of their ratio as a function of cluster redshift. My hypothesis is that the proportion of spiral to elliptical galaxies in these clusters approximately constant, but may show some signs of evolution over cosmic time. The Abell clusters that were observed tended to be towards the 50 percent spiral and 50 percent elliptical galaxies. This was due to a high-density bias that returns more elliptical than spiral galaxies. The random search that was conducted returned 67 percent spiral galaxies and 33 percent elliptical, which is right on with the universal percentages. It was also able to find a few high- density regions that were rich with elliptical galaxies. However, there was no significant evolution found over the redshift of z = 0 through z = 0.4.