The focus of this thesis is the study of stellar populations of extra-galactic glob-
ular clusters (GCs) by measuring spectral indices and comparing them to simple
stellar population models. We present the study of GCs in the context of tracing
elliptical galaxy star formation, chemical enrichment and mass assembly.
In this thesis we set out to test how can be determined about a galaxy's formation
history by studying the spectra of a small sample of GCs. Are the stellar population
parameters of the GCs strongly linked with the formation history of the host galaxy?
We present spectra and Lick index measurements for GCs associated with 3 el-
liptical galaxies, NGC 1052, NGC 3379 and NGC 4649. We derive ages, metallicities
and a-element abundance ratios for these GCs using the x2 minimisation approach
of Proctor & Sansom (2002).
The metallicities we derive are quite consistent, for old GCs, with those derived
by empirical calibrations such as Brodie & Huchra (1990) and Strader & Brodie
(2004). For each galaxy the GCs observed span a large range in metallicity from
approximately [Z/H]=�2 to solar.
We find that the majority of GCs are more than 10 Gyrs old and that we can-
not distinguish any finer, age details amongst the old GC populations. However,
amongst our three samples we find two age distributions contrary to our expecta-
tions. From our sample of 16 GCs associated with the 1-2 Gyr old merger remnant
NGC 1052, we find no young GCs. If a significant population of GCs formed during
this merger we would expect those GCs to have low mass-to-light ratios and be
included in our sample of bright GCs. We find 4 young GCs in our sample of 38
around NGC 4649, an old massive cluster elliptical. There are no signs of recent
star formation and therefore we do not expect any GCs to have formed within the
galaxy. These results seem to indicate that the GC systems of elliptical galaxies are
not strongly associated with recent field star formation.
We find a correlation between the α-element abundance ratio and the metallicity
for all three samples. Using Thomas, Maraston & Korn (2004) models, we measure
much higher α abundance ratios for low metallicity GCs than high metallicity GCs.
With current data and models we are limited in both the accuracy and the detail
with which we can probe this relationship.
We suggest that there are some difficulties reconciling measured GC parameters
with our expectations and propose some future work which could help to resolve
these and other issues.
| Identifer | oai:union.ndltd.org:ADTP/216651 |
| Date | January 2006 |
| Creators | Pierce, Michael John, n/a |
| Publisher | Swinburne University of Technology. |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.swin.edu.au/), Copyright Michael John Pierce |
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