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 H n/Fe-in the integrated light of a sample of 100 field and cluster E/SO gala xies. The measured indices are sensitive to age and/or metallicity variatio ns within the galaxy sample. Using linear regression analysis for data with nonuniform errors, we determine the intrinsic scatter present among the sp ectral indices of our galaxy sample as a function of internal velocity disp ersion. Our analysis demonstrates that there is significantly more intrinsi c 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 o f 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.