Leo Blitz
(UC Berkeley)
Star Formation and Neutral Gas in Normal Galaxies - Leo Blitz Colloquium
Great strides have been made in galaxy evolution in the last decade
through a combination of improved observations, semi-analytic modeling
of galaxy evolution, and simulations. Nevertheless, one of the
biggest gaps in our knowledge has to do with how stars form on
galactic scales. How does the number and distribution of new stars in
galaxies get established? How does this change as a function of
redshift? What is the role of "feedback," i.e. mass expulsion? How
ubiquitous is the IMF? I will take the position that the distribution
and state of the interstellar gas is paramount in answering these
questions. I will describe several well-known observational facts
about the distribution of atomic gas in spiral galaxies that have no
agreed upon explanation.
We will see that the neutral gas, the atomic plus the molecular,
follows an approximate scaling relation. I will discuss the molecular
gas depletion time problem in spiral galaxies, and some of the
implications for galaxy evolution, and a possible solution. I will
show that what determines how the star forming material, the dense
molecular gas, is formed in galaxies, is hydrostatic pressure, and I
will show how this relates to galaxy scale star formation.
|
