Investigation of Changes in Emission Lines from Galaxies Through Time

We investigate the percentage of galaxies with strong emission lines at increasing redshift. From the Sloan Digital Sky Survey we selected 327,327 galaxies at varying redshifts, z. We then grouped the total number of galaxies by absolute magnitude, compared them with those that had strong Hα, OIII, and other relevant emission lines, and looked for the trend of shifting emission lines with z. We found a general trend of a drop in the percentage of galaxies with strong emission lines from z = 0.2 to z = 0.5, spanning from about 2.5 Gyr to 5 Gyr ago. We are not sure why this is happening, whether there is a bias of the data set with how galaxies are selected or how the data was observed, or whether this is a product of a real effect.