Compact Stellar Systems in Galaxy Clusters and Groups

Peter Firth (2008). Compact Stellar Systems in Galaxy Clusters and Groups PhD Thesis, School of Physical Sciences, The University of Queensland.

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Author Peter Firth
Thesis Title Compact Stellar Systems in Galaxy Clusters and Groups
School, Centre or Institute School of Physical Sciences
Institution The University of Queensland
Publication date 2008-11
Thesis type PhD Thesis
Total pages 208
Subjects 240000 Physical Sciences
Formatted abstract
Compact stellar systems (CSSs) are spheroidal collections of between several thousand and tens
of millions of stars, found through wide field point source surveys in galaxy clusters. At least
an order of magnitude fainter and smaller than dwarf galaxies, CSSs are potential fossil records
of the galaxy cluster assembly process and may partly account for the discrepancy of up to two
orders of magnitude between the predicted number of dark-matter dominated dwarf galaxies
and the lesser number observed. We have classified CSSs into sub-populations – the numerous
low luminosity globular clusters (GCs) that closely surround and are gravitationally bound to
giant elliptical galaxies; the larger, high luminosity ‘ultra-compact dwarfs’ (UCDs) which we
refer to as luminous CSSs; and intracluster globular clusters (IGCs) not bound to any large
galaxy. The aim of this thesis is to determine the distribution and origins of luminous CSSs in
environments ranging from the dense cores of galaxy-rich clusters to poor galaxy groups, and
to determine if a true population of isolated IGCs exists.
This thesis is based on wide-field, multi-fibre and long-slit spectroscopic observations in
the nearby (D < 25Mpc) Fornax and Virgo galaxy clusters, and in six nearby galaxy groups.
These observations were made between 2004 and 2007 at the Very Large Telescope in Chile,
the Anglo-Australian Telescope in Australia, and the Gemini-North Telescope in Hawaii. Our
observations have surveyed and provided redshift information on several thousand point source
CSS candidates. We also obtained high signal-to-noise spectra of CSS examples in both clusters.
We found new CSSs in the galaxy clusters – notably the first spectroscopically confirmed
IGCs located far from any large cluster galaxy. We show that (1) luminous CSSs in the Fornax
Cluster core regions are dynamically relaxed compared with typical GCs and dwarf galaxies;
(2) Fornax has more luminous CSSs than Virgo, even after scaling for cluster mass; (3) the
broadband colours of Fornax luminous CSSs extend further towards the red than those in
Virgo, reflecting the higher average metallicity of Fornax CSSs; (4) luminous CSSs in cluster
core regions are generally ancient with sub-solar metallicity, but some are atypically young
and/or metal-rich; (5) there is evidence of a population of IGCs in Virgo.
We conclude that galaxy clusters contain several sub-populations of luminous CSSs. Thebright tail of the GC distribution, accumulated through galaxy mergers and now surrounding
the central giant elliptical galaxies in Virgo and Fornax, formed in the early Universe. An additional
sub-population in the Fornax cluster core formed more recently through tidal stripping
of dE,Ns by the central galaxy, or in gas-rich galaxy mergers. The sizes of these luminous CSS
sub-populations depend on both cluster mass and the extent of dynamical relaxation in the
Future research should seek to enlarge the luminous CSS and IGC catalogues by employing
larger ground-based telescopes for redshift surveys at fainter limits and in more distant galaxy
clusters; search for tidal star tails around known luminous CSSs using deep imaging by a spacebased
optical telescope such as HST; and obtain age and metallicity information on a larger
proportion of known luminous CSSs.
Keyword stellar systems, galaxies, clusters, groups, Virgo Cluster, Fornax Cluster, redshift.

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Created: Thu, 04 Dec 2008, 09:10:19 EST by Mr Peter Firth on behalf of Library - Information Access Service