Galaxies 09: Assembly, Gas Content and Star Formation History of Galaxies
Jonathan Tan
University of Florida
General Theory of Star Formation
Star formation theories require close guidance from observations and
numerical experiments. I review recent theoretical and observational
progress in our understanding of how star formation proceeds. With the
aim of understanding galactic scale star formation rates, I start with
what we are learning from detailed studies of Galactic star-forming
regions. Individual stars appear to form from gas cores that have a
mass spectrum comparable to the stellar initial mass function. Star
formation is highly clustered within turbulent giant molecular clouds.
Studies of mid-infrared dark clouds are revealing important
information about the earliest phases of star cluster formation. I
discuss the timescale of star cluster formation and review the
evidence that it is long compared to the free-fall time of the natal
gas clump. In this case, the gas clump can be considered to be
globally in near virial and pressure equilibrium, with turbulence
driven internally by protostellar outflows. Returning to the earliest
phases of star cluster formation, I consider the physical mechanisms
that may initiate the process, including compressions induced by ISM
turbulence, GMC collisions and stellar feedback. I compare predictions
of these theories for the radial profiles of SFRs in disk galaxies
with observed systems. I conclude by discussing how these theories
extend into the starburst regime.
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