Spectroscopic Gradients in Elliptical Galaxies
Abstract
Preliminary results based on a large compilation of line-strength profiles are presented and discussed. Elliptical galaxies (Es) with strong central Mg2 show steeper line-strength gradients. These galaxies are more massive and have higher velocity dispersions, note nevertheless, that the Mg2 gradient correlates better with central Mg2 than with any other global or structural parameter. This correlation, and the fact that Mg2 measures Z/Z together with the [Mg/Fe] abundances among Es, are of extreme importance for the use of the central Mg2-σ relation as a reflection of a mass-metallicity relation. Spectroscopic gradients arise mainly from a radial decrease in mean stellar metallicity. However, the Mg2 and < Fe> gradients do not correlate within measuring errors, indicating that something else, besides metallicity, is also varying within a galaxy. Hβ gradients indicate that the centers of Es tend to look spectroscopically ``younger'' than their stellar populations further out.
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