Title: Two phase formation of galaxies
Speaker: Jeremiah Ostriker
Institute: Princeton University
Time: September 16, 10:am-11:30am, 2009
Location: seminar hall 135
Now that we have a quite definite cosmological model, providing us with a quantitative picture of how perturbations grew from very low amplitude Gaussian fluctuations, we can perform the forward modeling of representative pieces of the universe using standard physical processes to see how well our computer simulations match real, locally observed systems. Finally, we can employ large ground and space based telescopes to use the universe as a time-machine - directly observing the past history of our light-cone comparing with our computed evolutionary tracks. A coherent and plausible picture is emerging with massive galaxies forming in two phases. In the first phase, which peaks at redshift z = 6 and ends by redshift z = 2, cold gas streams in, making stars in a small (<1kpc) region, but as the stellar mass approaches 10^{11} Msolar, a hot bubble forms which suppresses further inflow of cold gas. Later, from redshift z = 3 to the present time, smaller stellar satellite systems are accreted at typically 10kpc from the center and the size of the total system grows by about a factor of three as the mass doubles. This added, accreted component is mainly comprised of old and low metallicity stars. Energy release from gravitational infall in various forms will terminate star-formation even in the absence of feedback from SN or MBHs. This physical picture seems naturally to lead to the mass, size, scale and epoch of galaxy formation.
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