Star formation appears to proceed dynamically at both small and large scales. I will summarize the evidence for small scale dynamical formation in supersonic turbulent flows, and examine how well such flows can resist gravitational collapse. I will then present high-resolution simulations of star cluster formation in a wide range of isolated disk galaxies, using a three-dimensional, smoothed particle hydrodynamics code with an isothermal equation of state and no explicit further feedback. Despite the simplicity of our assumptions, our models quantitatively reproduce not only observed global and local Schmidt laws (relationships between gas surface density and star formation rate), but also observed star formation thresholds in disk galaxies. We can derive the global star formation efficiency in galaxies as a function of their stability. Our results suggest that the dominant physical mechanism determining the star formation rate is just the strength of gravitational instability, with feedback primarily functioning to maintain a roughly constant effective sound speed in the gas. We then use the same technique to study star cluster formation in a galaxy merger. For the first time in such a simulation, individual star clusters are directly identified and followed on their orbits. We quantitatively compare star formation in the merger to that in the unperturbed galaxies. The merging galaxies show a strong starburst, and produce clusters with the high specific frequency and bimodal distribution of metallicity observed in elliptical galaxies. I'll end with a visualization of coming attractions: the merger of the Milky Way and Andromeda.
Tuesday, November 1st
Seminar is to be held at 4:00 PM in the conference room
on the second floor of Dearborn Observatory
Refreshments will be served at 3:30
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