Olszewski is currently pursuing two major research efforts, along with a number of other projects.
1) Mass modeling of dwarf spheroidal galaxies: These galaxies have no gas and are dominated by their non-baryonic component (dark matter), so the baryons (stars) are test particles in a very simple gravitational potential, that of the dark matter. Knowing the central and global distributions of the dark matter, and measuring the extent of the dark matter, we can test models of the evolution of structure of the universe as well as limiting the properties of the dark matter. [Major collaborators are Mario Mateo [Michigan] and Matthew Walker (Harvard).]
We are also measuring the orbits (proper motions) of the family of Milky Way dwarf spheroidals. These orbits are determined from multi-epoch HST imaging of fields in these galaxies with a background quasar along the same line of sight to determine the zero-motion frame. This gives us a handle on the tidal history of these objects, how they might have become spheroidal and gas-free, and how far along they might be in the process of being destroyed. [ Major collaborators are Tad Pryor (Rutgers) and Slawomir Piatek (New Jersey Institute of Technology.]
2) Structure and star formation histories of the Large and Small Magellanic Clouds: Modern orbits derived by another group (Kallivayalil et al.) and reanalyzed by us, from multi-epoch HST observations, imply that the Magellanic Clouds are late-comers to the Milky Way neighborhood. They are now near the end of the process of falling into its sphere of influence for the first time. They have not, as once thought, been orbiting the Milky Way for most of a Hubble time.
Coupling new theoretical models by Gurtina Besla (Columbia) with our observational surveys allows us to see how the structure of the outer parts of the Clouds should be affected. The problem is, to survey the entire pair of Magellanic Clouds to levels fainter than the main-sequence turnoff of a globular-cluster-age population takes more observing time than current telescopes can offer. That said, we have done a 1%-filling-factor survey (The Outer Limits Survey, an NOAO survey project) in specially picked regions of both Magellanic Clouds, to understand the star formation and tidal histories of these extremely low-density regions. A set of fields to the North of the LMC center, extending out to 22° shows a perfect exponential disk out to ~12 inner-disk scale lengths. This implies a rather quiet tidal history (the LMC and SMC are interacting, which is probably the major source of tidal distortions at this moment). Furthermore, in all fields beyond ~9° from the center of the LMC, the dominant population is ~8 Gyr old. What is special about 8 Gyr? [Major collaborators are Abhijit Saha (NOAO), Knut Olsen (NOAO), Tim Axelrod (Arizona/LSST).]
3) We are also investigating the large-scale structure of individual Milky Way globular clusters after discovering that NGC 1851 can be traced to a radius of ~250 pc. Is this a remnant nuclear star cluster in a now-destroyed dwarf galaxy? [Major collaborators are Abhijit Saha (NOAO) and Tim Axelrod (UA/LSST).]
We are setting up fundamental photometric (19th mag hot DA white dwarfs) standard star system using HST photometry and Gemini spectra, for use with LSST and present and future deep surveys. [This effort is being led by Abhijit Saha (NOAO) and Chris Stubbs (Harvard).]
We are beginning a project to determine if the MACHO source stars in the LMC are actually SMC stars wrapped behind the LMC as predicted by Besla. [Major collaborators are Tim Axelrod (UA/LSST), Abhijit Saha (NOAO), Knut Olsen (NOAO).]