Date of Award
Doctor of Philosophy (PhD)
William E. Harris
I have undertaken a systematic survey of 12 dwarf elliptical (or dE) galaxies in order to find and study their globular cluster systems (GCS's). The sample represents both nucleated and non-nucleated dE's in the: Virgo cluster and near NGC 3115. In 10 of the galaxies observed, we have detected a likely GCS as a > 1σ excess of stellar-like objects.
The mass spcctrum (dN/dm) of the GCS's around NGC 3115 DW1 and for 8 Virgo dE,N's have slopes of ~ -1.8 to -1.9, in very good agreemcnt with that observed for GCS's around larger galaxies. This suggests that globular clusters formed via the same mechanism in galaxies of all masses and morphologies. In accordance with the recent work of Harris & Pudritz (1994), these results are also consistent with the picture where GC's formed in the cores of supergiant molecular clouds.
For the 12 dwarfs for which specific frequencies (SN) were derived (and 5 more for which similar information is available) the mean SN is ~ 4, consistent with that observed in giant elliptical galaxies (indicating similar formation efficiencies) and in Local Group dE's, although much larger than in spirals. There is no significant difference in SN between the nucleated (dE,N) and non-nucleated dE's, supporting evidence that they are similar types of object, and not the result of strongly different evolutionary paths. The higher SN values (~ 25) in two low luminosity dwarfs may be due to significant mass loss at various epochs.
In 3 galaxies for which I have color information, thc GC's arc bluer (in the mean) than tthat of thc galaxy light, suggcsting that the clusters are more metal-poor (by ~ 0.5 dex in [Fe/H]) than the galaxy halo stars, as observed in giant galaxies. However, the presently observed GCS would have been unable to create this offset; it would likely have arisen from a combination of a shallower IMF, other sites of star formation, and all initially larger globular cluster population.
Durrell, Patrick R., "Globular Cluster Systems in Dwarf Elliptical Galaxies" (1996). Open Access Dissertations and Theses. Paper 4012.