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The halos of galaxies are prime snooping grounds for understanding their assembly
histories. Globular clusters (GCs) in particular may be used to trace both the star
formation history and the dark matter (DM) content of galaxies and groups of galaxies. Our
"SAGES"
research group is engaged in an unparalleled wide-field photometric and spectroscopic
survey of nearby galaxies, "SLUGGS", focusing on GCs but also matching them with
constraints from field stars, planetary nebulae (PNe), and hot X-ray gas emission. We have
various projects available according to the student's interest, including exploiting
observations from Keck, VLT, Subaru, Magellan, MMT, etc.; and theoretically-oriented
dynamical modeling.
Some sample observationally- and theoretically-oriented first/second-year projects are detailed below to illustrate the possibilities. There are also options for very-short-term getting-your-feet-wet projects at the start of the school year. |
Observational: Extraordinary dark matter in an ordinary elliptical?
Recent work has questioned standard assumptions about dark matter in "ordinary" elliptical galaxies, using PNe as kinematical tracers to probe the mass content of the galaxy halos. This controversial result calls for clearer observational constraints, and we are focusing on the keystone galaxy known as NGC 4697, where we have obtained spectra of PNe and globular clusters much farther out into the halo of this galaxy than ever before. The goal of the student project will be to reduce and analyze these spectra (along with associated photometry), providing critical insight into the DM content of ordinary ellipticals. Starting with a basic knowledge of unix-type commands, the research will be carried out using the standard IRAF reduction software as well as with more specialized packages. The student will thus obtain a working knowledge of some of the most fundamental techniques and software in astronomical photometry and spectroscopy, and will acquire a basic ability to model the gravitational dynamics of a galaxy. If the project is successful, a paper of high impact will result. There is also ample scope for the student to go on a Keck observing run to acquire new data.
Theoretical: Ellipticals as a battleground in the dark matter and gravity wars
For almost as long as dark matter has been recognized as a pervasive component in the universe, another viable possibility has persisted: that the mass discrepancies found in various systems are due not to an exotic component of matter, but to a radical revision of the law of gravity, with the MOdified Newtonian Dynamics (MOND) as the leading contender. After being well-established in the realm of spiral galaxies, MOND awaits critical tests among elliptical galaxies, where the hodge-podge of results so far are both supportive and dismissive of MOND. There is thus a pressing need for a unified MOND-based analysis of the available constraints in ellipticals, which may resolve questions about the universal consistency of MOND once and for all.
The student will begin by assembling an inventory of "mass profiles" of elliptical galaxies from the literature, as derived via tracers such as GCs, PNe, and X-ray emission. The profiles will be fitted retroactively with a MOND force-law in order to determine the necessary MOND parameters and any residual DM. Depending upon the results, the student will next study basic MOND scaling relations of a large sample of galaxies, or explore the dynamical models of individual galaxies in more detail. To pursue this research requires a basic command of unix as well as facility with a computational language such as C or Mathematica. The student will gain experience with concepts and techniques in numerical and statistical analysis, and with theoretical dynamics, and will have exposure to observational data. A successful project should result in a milestone paper in the field of MOND studies.