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Research projects and interests.

Note: The following is an informal explanation of my research. For formal discussion, please see my [CV] for a list of papers and presentations on these and other topics.

Project: HVCs

I'm currently working with Mike Shull on high velocity clouds (HVCs). These are mysterious objects first detected through Hydrogen (HI 21cm) absorption features, characterized by large velocities with respect to "normal" galactic rotation. They can be seen in most of the sky (~81%; see Shull et al. 2009, in press), and indeed around at least one other spiral galaxy, M31. They have fairly low metallicity (~10-30% solar) and, with data from both FUSE and Hubble STIS, we find that they often have components that show low ions, such as CII, SiII, and OI. However, some also show absorption in high ions, like OVI, CIV, SiIV, SIV, etc.

The main goals of our research are to:

  1. determine the source of the clouds (a reasonable guess is the mixing of outblown galactic gas and primordial gas above the halo) and how they are moving with respect to the galaxy
  2. constrain what the probable cause of the multiphase state of the gas through photoionization modeling (i.e., could the gas be falling into the disk, creating a shock that heats the outer envelope and collisionally ionizes it?), and
  3. estimate how much gas is falling into the galaxy. A nagging problem for astronomers has been finding out how the galaxy keeps forming stars when so much gas is continuously being "locked up" in small stars, like ours; if HVCs are massive enough, their falling into the disk of the galaxy could explain how star formation has continued.

Project: Coma cluster

Another research topic I'm working on, with Ann Hornschemeier of Goddard Space Flight Center, is the red sequence of the Coma cluster of galaxies. This rich, nearby neighborhood (z ~ 0.02) provides an excellent opportunity to study large numbers of galaxies and how they interact. The red sequence is a place in color-magnitude space to which galaxies tend to evolve after entering a cluster environment. Using photometric data from the Spitzer Infrared Array Camera (IRAC) and the Sloan Digital Sky Survey (SDSS), as well as reliable, optical redshifts from the MMT Hectospec telescope (to determine cluster membership), we generate near-IR-optical colors and examine the extent to which galaxies lie on the red sequence. We also look at galaxies that lie off the red sequence with 3-sigma significance, as these could be an interesting subset of infalling galaxies, AGN, etc.

Research Interests

My past research topics include:

  1. Asteroid photometry: determining rotation periods via small-telescope photometric light curves
  2. Cataclysmic Variables: constraining properties (disk temperature, quasi-periodic trends in quiescence), via optical colors, of dwarf nova SS Cygni
  3. IR and Optical photometry of the Coma Cluster
  4. UV Spectroscopy of HVCs

In addition, I'm interested in instrumentation work, other galactic and extragalactic astrophysics projects, and cosmology - not to mention science policy and science education.