Are Small Ellipticals Younger Than Big Ellipticals?

Details Are Small Ellipticals Younger Than Big Ellipticals? Are Small Ellipticals Younger Than Big Ellipticals?

Dec 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...183.4205t&link_type=abstract

American Astronomical Society, 183rd AAS Meeting, #42.05; Bulletin of the American Astronomical Society, Vol. 25, p.1354

Astronomy and Astrophysics

Astronomy

4

Scientific paper

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 Hβ 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 Hβ 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 ~ 3\ Gyr to greater than 15\ Gyr. Furthermore, weak-lined galaxies (Mgb < 4 Angstroms) 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.

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