Statistics – Computation
Scientific paper
Oct 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt.........9c&link_type=abstract
Thesis (PhD). THE UNIVERSITY OF WISCONSIN - MADISON, Source DAI-B 62/04, p. 1901, Oct 2001, 302 pages.
Statistics
Computation
1
Scientific paper
In this thesis I address the formation and evolution of low-mass galaxies, and investigate their importance in the general galaxy evolution/formation process. Currently favored models of galaxy formation, such as Cold Dark Matter, suggest that the first galaxies to form in the universe have low masses and sizes, similar to modern dwarf galaxies, that later merge to form more massive systems. The most common galaxy in the nearby universe are dwarf ellipticals in clusters that could be descendents of these early galaxies. This thesis address two questions related to these objects: (1)are the dwarf ellipticals seen in clusters an old primordial population that survived since their initial formation, or are these dwarfs the end product of some evolutionary dynamical process? and (2)do galaxy mergers occur in the universe, and if so, how does this merging evolve through time? To determine if dwarf ellipticals are an old cluster population, kinematic, structural and photometric information for these objects was obtained using the WIYN 3.5m telescope. Radial velocities of dwarf ellipticals in the Virgo cluster suggests that these objects are not an old cluster population, but were accreted sometime in the past. Kinematics also demonstrate that these objects could have originated from a more massive progenitor. Photometry of dwarf ellipticals in the Perseus cluster further suggests that the stellar populations of these objects are old, with little to no recent star formation, or population gradients. The broad-band UBR colors of these objects are also consistent with color differences originating from metallicity. Low-mass, or dwarf galaxies in the Perseus cluster however do not follow the color- magnitude relationship found for giant ellipticals, with some too red and others too blue for their magnitudes. By comparing with ΛCDM models of galaxy formation, I show that the objects too blue for their colors are consistent with being old CDM galaxies. Low mass cluster galaxies that are too red are consistent with having originated from the bulges of spiral galaxies induced by mass loss from high-speed impulsive interactions with other cluster galaxies. To address the issue of galaxy mergers, I develop and use a morphological system to identify robustly, and unambiguously, objects undergoing major mergers. This system uses the asymmetry index, such that galaxies undergoing mergers have asymmetry values A > 0.35. Applying this to the galaxies in the Hubble Deep Field, an increase with redshift of galaxies undergoing mergers is found. Depending on the method of computation, the merger fraction evolution out to z ~ 3.5 can be characterized as f = (1 + z)m, where m ranges from 1 to 2.5. The best fit gives a variable m, such that m = 2.96-0.32 × z. Finally, I investigate the properties of a nearby massive central cluster galaxy, NGC 1275 in the Perseus cluster, whose unusual properties and salient structural aspects can be partially accounted for by recent and past mergers.
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