University of California, Irvine
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How Galaxies Form Stars
University of Chicago
Observed star-forming galaxies convert their gas into stars inefficiently. The typical time on which available gas in galaxies is depleted is ~5-10 Gyr which is orders of magnitude longer than any physical timescale relevant for star formation. The origin of long depletion times is a long-standing puzzle. Many galaxy simulations can reproduce observed long depletion times but the physical mechanism controlling their values is not understood. In addition, some of the simulations show rather counter-intuitive behavior: global depletion times appear to be almost insensitive to the assumptions about local star formation in individual star-forming regions, a phenomenon described as “self-regulation.” Yet another part of the puzzle is the observed tight and near-linear correlation between star formation rates and the amount of molecular gas on kiloparsec and larger scales. A linear correlation implies that depletion time of molecular gas is almost independent of molecular gas density on >kiloparsec scales, while popular models of star formation in galaxies predict a strong dependence. I will present results from a suite of isolated disk galaxy simulations in which we systematically explored the behavior of depletion times. Using insights from these simulations we formulated a physical model that explains both the origin of long gas depletion times in observed galaxies and the results of galaxy formation simulations. This model also sheds light on the origin of the observed linear correlation between star formation rates and molecular gas.
Host: Hui Li