http://arxiv.org/abs/1409.1598
What turns star formation on and off in large galaxies, and what regulates their star-formation rates? These questions are central to modern studies of galaxy evolution and are particularly acute for the universe’s largest galaxies, which reside at the centers of galaxy clusters. Roughly one-third of those central galaxies are currently forming stars at 10-100 times the observed rates; the other two-thirds show no evidence for star formation. Here we present a comparison of theoretical models with optical and X-ray data that explains this star-formation dichotomy and confirms for the first time that precipitation of cold clouds out of the hot gas is what triggers the feedback response that regulates star formation. Some of the precipitating clouds form stars while others accrete onto a central black hole, releasing energy that heats the surrounding atmosphere and limits further precipitation. Large bursts of feedback or mergers with other galaxy clusters can shut off precipitation and stop star formation if they enable thermal conduction to outcompete radiative cooling of the hot atmosphere and eradicate cool clouds left over from previous precipitation cycles.
G. Voit, M. Donahue, G. Bryan, et. al.
Mon, 8 Sep 14
42/69
Comments: Submitted to Nature 3 Sep 2014