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Title:
Differential Spectral Synthesis of Low-Luminosity Elliptical Galaxies
Authors:
Jones, Lewis Alexander
Affiliation:
AA(THE UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL)
Publication:
Thesis (PHD). THE UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL , Source DAI-B 60/07, p. 3325, Jan 2000, 257 pages.
Publication Date:
00/1998
Category:
Physics: Astronomy and Astrophysics
Origin:
UMI
Comment:
Publication Number: AAT 9938165; Advisor: ROSE, JAMES A.
Bibliographic Code:
1998PhDT.........3J

Abstract

In this thesis, a study of the spectral variations in the integrated light of eight low-luminosity elliptical galaxies is presented. The unique opportunity provided by low-luminosity elliptical galaxies to study integrated spectra at high line definition is the motivation behind the observational approach for this study. A long wavelength baseline is sacrificed in favor of working at high resolution (~2 Å FWHM) with a large variety of narrow absorption features in a smaller wave-length window. A new spectral library has been developed with this approach in mind. The library consists of spectra of 684 stars all observed with the Coudé Feed Telescope and Spectrograph at the Kitt Peak National Observatory, covering the spectral ranges 3820-4500 Å and 4780-5450 Å and at a spectral resolution of ~2 Å FWHM. The coverage of the library is complete for spectral types A-K and luminosity classes I-V, in the range -2.5 <= FeH; <= +0.5, while the O, B, and M stars are near solar. The empirical investigation of the galaxy spectra in reference to the stellar sequences of the spectral library yields several key results. (1) There is a spread in the mean spectral types of the low-luminosity ellliptical galaxies. (2) The galaxies are similar in evolved star content, Fe line strengths, and their evolved star light is dominated by solar type giants. (3) Five of the eight galaxies are shown to contain less than a 5% hot star contribution, which is inconsistent with the prediction of ~10% from the simple model of chemical evolution (Worthey, Dorman, and Jones 1996). (4) From variations in the balance of dwarf and giant light in the galaxy spectra it is claimed that there is a spread in the mean stellar ages of the low-luminosity elliptical galaxies. These results are interpreted in the context of the evolutionary synthesis models of Worthey (1994). The main result from the comparison of the galaxies and models is that the low-luminosity elliptical galaxies show a large spread in mean age, spanning the entire Hubble time, while covering only a narrow range in metallicity. Not only are the basic empirical results reproduced in the models, but it is shown that the balance of dwarf and giant light in the spectrum, as well as mean galaxy spectral type, correlates well with age at constant metallicity.
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