Population Studies in Groups and Clusters of Galaxies.
Abstract
Studies of galaxies and clusters of galaxies provide some of the best observational constraints on theories for the origin and evolution of the universe. However, most studies carried out to date have been biased toward galaxies with high luminosities, which are rare compared to low-luminosity, low-surface-brightness dwarf galaxies. To begin to redress this bias, we have carried out a deep optical survey of six nearby groups of galaxies using 40 large-scale plates taken with the du Pont 2.5-m reflector at the Las Campanas Observatory, and have combined our catalogs with data from a similar study of the Virgo Cluster by Binggeli et al. (1985). By virtue of their low surface-brightness, dwarf galaxies in nearby groups can be readily distinguished from background galaxies. We confirm the well-defined relation between surface brightness and luminosity for the dwarf galaxies in our sample, and show that this relation does not result from selection effects. The dwarf-to-giant ratio varies significantly from group to group in our sample. The variation is most pronounced for the early-type (E, SO, dE, and dSO) galaxies; the Virgo Cluster contains five times as many early-type dwarfs per early-type giant as the poorest groups of galaxies in our survey. The dwarf to giant ratio shows a positive correlation with the richness of the groups. We find no significant variations in the dwarf -to-giant ratio with radius in the groups, or with local density. With one exception, the luminosity functions of the individual Hubble types appear to be independent of environment. The exception is the non-nucleated dE's. Non -nucleated dE's brighter than M_{B_ T} ~ -14.2 have the same spatial distribution in the Fornax and Virgo Clusters as the spirals and irregulars. The faint dE's, however, are much more centrally concentrated in these clusters. The shape of the dE luminosity function therefore varies with distance from the cluster center and with local density. The flattening distribution of the bright non-nucleated dE's is similar to that of the irregulars, suggesting a possible evolutionary connection between these two classes of galaxies.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1990
- Bibcode:
- 1990PhDT.........1F
- Keywords:
-
- VOLUMES I AND II;
- Physics: Astronomy and Astrophysics;
- Galactic Clusters;
- Galactic Evolution;
- Sky Surveys (Astronomy);
- Star Distribution;
- Stellar Luminosity;
- Astronomical Catalogs;
- Cosmology;
- Dwarf Galaxies;
- Populations;
- Reflecting Telescopes;
- Astronomy