University of Minnesota (2002 - 2006)

In 2002 I started my PhD at the University of Minnesota, continuing my work on neutral hydrogen in the Milky Way Galaxy. My PhD advisor was Dr. John Dickey. My project was an extension of the work I did for my masters. I expanded the dataset I analyzed to include the entire International Galactic Plane Survey (IGPS). In addition to the CGPS the IGPS consists of the Southern Galactic Plane Survey, and the VLA Galactic Plane Survey. Together these datasets cover over 260 degrees in longitude within several degrees of the Galactic plane centre.

For my PhD I developed a method to analyze individual absorption features to determine the cool-phase neutral hydrogen temperature. This allowed me to look at the global trends in temperature and other physical characteristics of the neutral hydrogen for the first time. In agreement with other recent work, I found temperatures mostly between about 30 K and 100 K, cooler than previously thought. I did not find a strong trend in temperature with distance from the Galactic centre (the Galactocentric radius) however: While the amound of cool-phase gas decreases with Galactocentric radius, the average temperature stays fairly constant around 50 K.

My PhD research also allowed me to look for the widespread presence of cool neutral hydrogen in the far outer Galaxy. As the pressure in the disk decreases we expect that eventually a cool medium can no longer be supported (if pressure equilibrium between the phases holds). I found that along most lines of sight that pass through the Galactic disk I saw cool-phase gas in the outermost spiral arms (the outer arm in the north, and a distant arm in the south) if my background sources are bright enough to yield a spectrum with low noise.

While at the University of Minnesota I used the VLA (picture on right) two times to obtain additional data. I also had the opportunity to travel to Green Bank (VW) and Granada (Spain) for summer schools on observing techniques. When John Dickey moved to Tasmania I went to visit him for a month in Tasmania, which was a highlight of my PhD both work wise as well as for the beautiful island I got to visit (my first and only trip to the southern hemisphere so far).

I was also heavily involved in public outreach and teaching in Minnesota. Every summer I participated in the "Universe in the Park" program, where we gave talks to the public and set up telescopes in parks around Minnesota. I gave presentations to diverse groups of people about various astronomical topics as well. I was also a volunteer for the International Wolf Center and the Science Museum of Minnesota.