Correlations between line strengths and fine structure in elliptical galaxies

Abstract

For 36 giant elliptical galaxies located mostly in the field and in groups, the strength of the nuclear Hβ absorption line at any given absolute magnitude increases systematically with the amount of fine structure (ripples, jets of luminous matter, X-structure, and boxy isophotes), while the strengths of the CN and Mg I + MgH features decrease. This effect is most likely due to systematic variations in mean age, rather than mean metallicity, of the stellar populations. We use the resulting correlations to estimate the contributions of age and metallicity variations to line-strength scatter and suggest that the elusive population of intermediate-age remnants of major disk-disk mergers may be found among ellipticals with much fine structure and enhanced Hβ absorption.