Are Small Ellipticals Younger Than Big Ellipticals?
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Session 42 -- Ellipticals
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

## [42.05] Are Small Ellipticals Younger Than Big Ellipticals?

S. C. Trager (UCO/Lick Observatory), S. M. Faber (UCO/Lick Observatory), J. Jes\'us Gonz\'alez (IA-UNAM), Guy Worthey (Univ. of Michigan)

We present a sample of Lick Image Dissector Scanner (Lick-IDS) nuclear spectral indices of elliptical galaxies. Galaxies which show noticeable [OIII] emission have been culled from the sample, as the presence of [OIII] may indicate filling-in of H$\beta$ stellar absorption by emission. The final, culled sample contains 87 ellipticals, of which 61 are galaxies not in the emission-culled sample of Gonzalez (1993). Of these, a sub-sample of 23 Virgo-cluster ellipticals over range of seven absolute magnitudes is identified, a six-fold increase over Gonzalez's (1993) study. The Lick-IDS metallicity indicators Mg and Fe plus the key H$\beta$ age index were measured. These were combined with model predictions of Worthey (1993) for co-eval generations of stars to estimate ages and metallicities of the stellar populations in each elliptical galaxy. In both the full sample of 87 galaxies and the Virgo sub-sample, ellipticals cover a wide range of ages, from $\sim 3\ Gyr$ to greater than $15\ Gyr$. Furthermore, weak-lined galaxies (Mgb$< 4$ \AA) are statistically younger and more metal-poor than strong-lined galaxies, confirming Gonzalez's (1993) results from a smaller sample. This is also true of the Virgo ellipticals, although this sub-sample is small. Comparing galaxy ages with various structural parameters, we find no trend in absolute magnitude with age, but low-velocity-dispersion ellipticals are statically younger than those with high velocity-dispersions. Some of these ellipticals are young enough that their stellar populations will look quite different even at moderate lookback times.