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“Star Formation and Neutral Gas in Normal Galaxies” Professor Leo Blitz UC Berkeley |
| Great strides have been made in galaxy evolution in the last decade through a combination of new and better observations, semi-analytic modeling of galaxy evolution, and simulations. Nevertheless, one of the biggest uncertainties has to do with how stars form on galactic scales. The role of "feedback," i.e. mass expulsion, the ubiquity of the IMF, star formation in the early universe, and how many stars form in normal galaxies are all open questions. In this context, I will describe six well-known facts about the distribution of atomic gas in spiral galaxies most of which have no known explanation. I will discuss the molecular gas depletion time problem in spiral galaxies, and some of the implications for galaxy evolution. I will show that what determines how the star forming material, the dense molecular gas is formed in galaxies, is hydrostatic pressure, and how this relates to the star formation within them. En passant, I will also review the first complete surveys of giant molecular clouds in nearby galaxies to see how the properties of the star forming material varies, and what this may mean for variations in the IMF. |