Dark matter halos and stellar kinematics of elliptical galaxies


Dark matter halos and stellar kinematics of elliptical galaxies

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dc.contributor.advisor Hill, Gary J.
dc.contributor.advisor Gebhardt, Karl
dc.creator Murphy, Jeremy David
dc.date.accessioned 2012-11-13T16:29:49Z
dc.date.available 2012-11-13T16:29:49Z
dc.date.created 2012-08
dc.date.issued 2012-11-13
dc.date.submitted August 2012
dc.identifier.uri http://hdl.handle.net/2152/ETD-UT-2012-08-6019
dc.description.abstract The hierarchical assembly of mass, wherein smaller clumps of dark matter, stars, gas, and dust buildup over time to form the galaxies we see today in the local Universe through accretion events with other clumps, is a central tenet of galaxy formation theory. Supported by theoretically motivated simulations, and observations of the distribution of galaxies over a large range of redshift, the theory of hierarchical growth is now well established. However, on the scales of individual galaxies, hierarchical growth struggles to explain a number of observations involving the amount and distribution of dark matter in galaxies, and the timescale of both the formation of stars, and the assembly of those stars into galaxies. In this dissertation I attempt to address some of the central issues of galaxy formation. My work focuses on massive elliptical galaxies and employs the orbit-based, axisymmetric dynamical modeling technique of Schwarzschild to constrain the total mass of a galaxy to large radii. From this starting point a determination of the extent and shape of the dark matter halo profile is possible and can then be compared to the results of simulations of the formation of galaxies. These dynamical models include information on the stellar orbital structure of the galaxy, and can be used as a further point of comparison with N-body simulations and observations from other groups. Dynamical modeling results for both M49 and M87, the first and second rank galaxies in the Virgo Cluster, are presented and compared in Chapters 4 and 2 respectively. Although both galaxies are similar in mass, a closer analysis shows they exhibit very different dark matter halo profiles and stellar orbital structure, and likely followed very different formation pathways. My primary dataset comes from observations carried out on the Mitchell Spectrograph (formally VIRUS-P) at McDonald Observatory.\footnote{The instrument's name was changed over the last year. As some of this work was originally written when the instrument was named VIRUS-P, I have elected to use that name in those sections of this dissertation (Chapters 2 and 5). In Chapters 3, 4, and 6, I use the current name.} The Mitchell Spectrograph is a fiber-fed integral field spectrograph, and allows one to collect spectra at many positions on a galaxy simultaneously. With spectroscopy one is able to not only constrain the kinematics of the stars, but also their integrated chemical abundances. In the introduction I describe recent work I have carried out with my collaborators using the Mitchell Spectrograph to add further constraints to our picture of galaxy formation. In that work we find that the cores of massive elliptical galaxies have been in place for many billions of years, and had their star formation truncated at early times. The stars comprising their outer halos, however, come from less massive systems. Yet unlike the stars of present day, low-mass galaxies, whose star formation is typically extended, these accreted systems had their star formation shut off at high redshift. Although our current sample is relatively small, these observations place a rigid constraint on the timescale of galaxy assembly and indicate the important role of minor mergers in the buildup of the diffuse outer halos of these systems. All of these advances in our understanding of the Universe are driven, in large part, by advances in the instrumentation used to collect the data. The Mitchell Spectrograph is a wonderful example of such an advance, as the instrument has allowed for observations of the outer halo of M87 to unprecedented radial distances (Chapter 3). A significant component of my dissertation research has been focused on characterizing the fiber optics of both the Mitchell Spectrograph and the fiber optics for the VIRUS spectrograph. I cover the results of the work on the Mitchell Spectrograph optical fibers in Chapter 5. The affects of stress and motion on a fiber bundle, critical to the VIRUS spectrograph, are explored in Chapter 6.
dc.format.mimetype application/pdf
dc.language.iso eng
dc.subject Dark matter
dc.subject Galaxy formation
dc.subject VIRUS
dc.subject HETDEX
dc.subject BCG
dc.subject M87
dc.subject M49
dc.subject Fiber optics
dc.subject Elliptical galaxies
dc.title Dark matter halos and stellar kinematics of elliptical galaxies
dc.date.updated 2012-11-13T16:31:08Z
dc.identifier.slug 2152/ETD-UT-2012-08-6019
dc.contributor.committeeMember Cappellari, Michele
dc.contributor.committeeMember Kormendy, John
dc.contributor.committeeMember MacQueen, Phillip
dc.contributor.committeeMember Milosavljevic, Milos
dc.description.department Astronomy
dc.type.genre thesis
dc.type.material text
thesis.degree.department Astronomy
thesis.degree.discipline Astronomy
thesis.degree.grantor University of Texas at Austin
thesis.degree.level Doctoral
thesis.degree.name Doctor of Philosophy

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