INTERMEDIATE BAND SURFACE PHOTOMETRY OF ELLIPTICAL GALAXIES.

摘要

The present structure of elliptical galaxies contains clues to the physical processes which played an important role in their early evolution. This dissertation reports on a program of detailed surface photometry of two normal elliptical galaxies, NGC 3379 and NGC 4406. The surface photometry was carried out with the Kitt Peak National Observatory Kron electronic camera, supplemented by conventional photoelectric photometry with the Yale-Cerro Tololo Interamerican observatory 40 inch telescope. The photometric system employed provided six indicies measuring a variety of absorption and continuum features.;A number of population syntheses have been carried out using the color profiles derived for NGC 3379. Most of the V band light in the resulting models is provided by late-type giants. If the CN band strengths in these stars correlate with their overall abundance levels, the models suggest that values of {Fe/H} (TURN) 0.4 may be reached near the center of this elliptical galaxy. Furthermore, metallicities may remain above solar out to a distance of 2.5 kpc from the center of NGC 3379. A source of blue light from either a few late A to late F main sequence stars or from a globular cluster population is required throughout NGC 3379.;The existence of an inflection point in the luminosity profile of the archetypal elliptical NGC 3379, first discussed by Burkhead and Kallinowski (1974), has been confirmed. The excess luminosity or bulge in the luminosity profile which gives rise to this inflection point can be adequately represented by a very broad gaussian. The parameters of this representation depend upon the bandpass in a manner consistent with the presence of an envelope gradient in NGC 3379.;The galaxy NGC 4406 is a Virgo Cluster elliptical and NGC 3379 is a Leo Group member. A study of the color profiles of these galaxies reveals two distinct classes of color and band strength gradients, a steep "core gradient" interior to a radius R/D(0) (TURN) 0.1 and an "envelope gradient exterior to this region. These gradients are in the sense that colors are redder and absorption features are stronger nearer the centers of the galaxies. The core gradient in NGC 4406 is much less prominent than that in NGC 3379. It is suggested that this is a result of differences in environment and evolutionary history.