University of Calgary (2000 - 2002)

In 2000 I went to the University of Calgary to work with Dr. Russ Taylor, a radio astronomer. My project was to analyze the neutral hydrogen gas in our galaxy, the Milky Way. I used data from the Canadian Galactic Plane Survey (CGPS). The CGPS is the largest surveys of neutral hydrogen gas with an angular resolution of close to 1 arc-minute. The wavelength at which neutral hydrogen emits light is 21 cm. The CGPS covers a strip along the Milky way with a width of about 10 degrees (20 moons) and a length of over 100 degrees (200 moons!).

Specifically, I used very distant points of light (mostly quasars) to study the temperature and density of the neutral hydrogen in the Galaxy. Somewhat like guessing the thickness of fog from the beams of an approaching car (which are partially absorbed by the fog) we can calculate the gas "optical depth" by studying the amount of absorption of the background sources. The more gas, and the colder it is, the more the distant source is absorbed.

For my masters thesis I computed the neutral hydrogen emission and absorption spectra toward 437 continuum background sources in the Canadian Galactic Plane Survey. Using these spectra I was able to compute a simple model of temperature variation in the Galaxy. Analyzing the column density, I found a roughly exponential drop with radius, with a local density increase in the Perseus arm region (around 13 kpc). I also found that the feature density clearly drops off with radius. In order to investigate the possible presence of a very cold neutral hydrogen component I investigated the correlation of the HI to CO. While there is no overall correlation, about 60 features are clearly visible in CO, indicating that at least some very cold HI exists.