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Past Research Programs
Research Interests:
- Tidal Dwarf Galaxies
- Compact Groups
- Galactic Structure
- Dwarf Satellite Galaxy Interactions
- Globular Cluster Dynamics
- Galaxy Formation and Evolution
- AGN (radio galaxies and blazars)
- Tidal Dwarf Galaxy Formation in Hickson Compact Groups: As a postdoc at Penn State, I studied Compact Groups in collaboration with Jane Charlton and Sally Hunsberger. In her thesis, Sally found that Hickson Compact Groups often show an excess of dwarf galaxy-sized objects compared to the field. We have been testing the hypothesis that dwarf galaxies may form in the multiple interactions that occur in compact groups by observing the candidate dwarf galaxies with the Hubble Space Telescope and the Hobby-Eberly Telescope. Our article on HST images of Seyfert's Sextet is in the November, 2002 issue of the Astronomical Journal. Recent results on the dwarf galaxies in Stephan's Quintet were presented at the January 2003 AAS meeting.
- The Ursa Minor Dwarf Spheroidal: A major portion of my PhD thesis was based on a wide field imaging survey of the Ursa Minor Dwarf Spheroidal. Covering approximately 10 square degrees, we imaged the dSph in the Washington M, Washington T2, and DDO51 filters. Using these three filters we isolate metal-poor giants accurately, and thus we are able to separate UMi stars from field stars with confidence. We have found that UMi appears to have a large population of stars outside its nominal tidal radius, leading us to believe that this dSph is being tidally disrupted by the Galaxy. Recently, we have been granted time with the WIYN telescope and Hydra multi-fiber spectrograph and the Keck telescope and the HIRES spectrograph to begin determing radial velocities for UMi stars far from the core.
- Extragalactic Analogues to the Sagittarius Tidal Stream: Recently, nearby spiral galaxies have been found to have rings of diffuse light surrounding them that appear to be qualitatively similar to the one produced by the Milky Way / Sagittarius dwarf interaction. We have been performing deep imaging of a sample of nearby spirals searching for similar giant spiral / dwarf satellite galaxy interactions. A nice example of this is visible in the Hubble Space Telescope ACS image of the Tadpole Galaxy.
- Milky Way Satellite and Globular Cluster Orbital Alignments: While I was considering various thesis topics, I began work on a side project that became the first part of my thesis (with Steve Majewski). We searched for fossil evidence of accretion events in the Milky Way halo. Assuming the Searle & Zinn picture of the halo having formed from accretion of fragments is correct, we should be able to find evidence of such accretion events in the current distribution of satellites in the halo. Support for this idea includes the Sagittarius dwarf, which shows signs of ongoing tidal disruption by the Milky Way, the alignment of the rest of the dwarf galaxy satellites along Lynden-Bell's two "Great Streams", and association of young second parameter globular clusters with the Sagittarius and Fornax dwarf galaxies. Assuming this picture is correct, we should find that satellites disrupted or created in a common tidal event should share similar orbital trajectories in galactic coordinates. We have therefore compared the distribution of the orbital parameters of certain subsamples of globular clusters and dwarf satellite galaxies searching for evidence of common orbital poles.
- The Pyxis Globular Cluster: Our analysis of the spatial and dynamical associations between globular clusters and Milky Way satellite galaxies suggests to us that the Pyxis globular cluster is a likely candidate to have been tidally torn from the Magellanic Clouds by the Milky Way. We have therefore begun the process of measuring its space motion by getting a radial velocity for several bright giants in the cluster. In addition, we were able to measure a spectroscopic metallicity for the brightest star, confirming the values derived photometrically by CMD fitting. Assuming the LMC capture origin is correct for Pyxis, we published a prediction for its proper motion given our measured radial velocity.
- The Giant FR II NVSS 2146+82: My Master's research project involved optical observations of the giant FR II radio galaxy, NVSS 2146+82. This object was discovered in the first field observed during the NRAO VLA Sky Survey (NVSS); an observation which occurred while I was an REU summer student at NRAO's VLA site in 1994.
As a group, the summer students were given VLA time to observe an object of our choice. Naturally, we chose to use our group time to observe this beast. It turns out that Alan Bridle and Bill Cotton have been following up on this object with the VLA, so I decided to look into the optical properties of the FR II host galaxy. With Dr. Steven Majewski I've observed the host in the UBVRI with the Palomar 60". Majewski and Matt Bershady also took spectra of the host as part of a separate observing program. Mike Siegel kindly donate 5 minutes of KPNO 4m time to get a few deep images in V and I, also. We have determined the redshift of the host to be z=0.145, indicating a linear size of 4 Mpc from lobe to lobe! What is the most interesting, though, is that this giant FR II appears to be near the edge of a dense group of galaxies, possibly of Abell richness class 0. An article is available in the May, 2000 issue of AJ (vol. 119, p. 2068) with the VLA maps, optical spectra, and optical photometry of the galaxy. In addition, we were awarded some ROSAT time (just prior to its untimely demise) to search for any hot IGM associated with the overdensity of galactic companions found associated with the host galaxy. Although we were unable to detect the IGM, our upper limit is consistent with the values found for other low redshift Abell Class 0 clusters containing FR II radio galaxies.