My Research Interests

At the moment, the majority of my research involves Damped Lyman α systems (more compactly known as DLAs). These are galaxy-scale objects found along the sight-lines towards more distant quasars. As a simple analogy, think of a quasar as a very bright (but very small) light source, and then think of a beam of light from the quasar passing through a galaxy on its way to us. These systems are interesting because they provide (in principle at least) an unbiased look at galaxy characteristics in the early universe (DLAs are selected simply by being between us an a quasar (randomly, that is) while other methods of detecting distant galaxies tend to be more sensitive to bright objects than faint objects, which can introduce a source of bias). Also, because we see DLAs in the light from a bright background source (the quasar), we can examine them in absorption (i.e. we can study the cold interstellar gas in the DLA because it absorbs some of the background light), which provides a useful complement to emission-based studies of galaxies.

My first DLA-related project has been a search for diffuse interstellar bands (DIBs, yet another acronym starting with D) in DLAs. The DIBs are a set of several hundred (some papers say “more than three hundred”, some say “over seven hundred”, but all agree that it’s in the hundreds) spectral absorption features associated with interstellar space (i.e. the absorbing molecule(s) are actually found in interstellar space, and not associated with stars). Since the DIBs were discovered back in 1922, many astronomers have tried to identify their source (which molecule(s) or dust grains were causing the DIBs), but so far without success. In searching for DIBs in DLAs, we hope to determine how the DIBs have evolved in other galaxies, and discover what that can tell us about their origin.

My second project has been looking at the spin temperature (T_s) of DLAs found towards radio-loud quasars. This involves comparing the UV Lyman-α line (sensitive to all the neutral hydrogen in the DLA) with the absorption at 21-cm (sensitive only to the cold neutral hydrogen) to determine the overall temperature of the interstellar medium (ISM) in the DLAs. While low-redshift (relatively close) DLAs show a variety of spin temperatures, both low and high, DLAs at higher redshifts have tended to show only high spin temperatures thus far. By greatly increasing the number of high-redshift DLAs with 21-cm measurements, we intend to determine how prevalent cold systems are at high redshifts.

Page last updated February 26, 2008

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