paper

The Shapes and Ages of Elliptical Galaxies

arXiv:astro-ph/9611104 · doi:10.1093/mnras/285.1.L1

Abstract

In this paper we investigate the relation between the detailed isophotal shape of elliptical galaxies and the strength of the H beta absorption in their spectra. We find that disky galaxies have higher H beta indices. Stellar population synthesis models show that the H beta line is a good age indicator, hence disky galaxies tend to have younger mean ages than boxy galaxies. We show that the observed trend can be brought about by a contaminating young population, which we associate with the disky component. This population need only account for a small fraction of the total mass, for example if a contaminating population of age of 2 Gyrs is superimposed on an old (12 Gyr) elliptical galaxy, then the observed trend can be explained if it contributes only 10% to the total mass. The size of this effect is consistent with the estimates of disk-to-total light ratios from surface photometry.

5 pages LaTeX, uses included mninp.tex and bib.sty and 4 PostScript figures. Accepted for MNRAS Letters. Also available at http://star-www.dur.ac.uk/~rdejong/papers.html

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