Spectral variations in early-type galaxies as a function of mass

We report on the strengths of three spectral indicators-Mg-2, H beta, and Hn/Fe-in the integrated light of a sample of 100 field and cluster E/SO galaxies. The measured indices are sensitive to age and/or metallicity variations within the galaxy sample. Using linear regression analysis for data with nonuniform errors, we determine the intrinsic scatter present among the spectral indices of our galaxy sample as a function of internal velocity dispersion. Our analysis demonstrates that there is significantly more intrinsic scatter in the two Balmer line indices than in the Mg, index, indicating that the Balmer indices provide more dynamic range in determining the age of a stellar population than does the Mg, index. Furthermore, the scatter is much larger for the low velocity dispersion galaxies, indicating that star formation has occurred more recently in the lower mass galaxies.