Rok Roškar: Learning about Galaxy Evolution from Outer Disks

Rok Roškar, University of Washington, Department of Astronomy

Learning about Galaxy Evolution from Outer Disks

Traditional theories of disk galaxy formation successfully predict that the light distribution in stellar disks should roughly follow an exponential radial profile. However, an abundance of recent evidence suggests that this is an oversimplification - many galaxies exhibit profiles, which deviate from a single exponential in the outer parts. We investigate this phenomenon with an N-body/SPH approach. First, we simulate a suite of idealized models representative of galaxy formation through dissipational collapse after the last major merger. Our approach is unique in that we allow the disk to form spontaneously from the collapse of the halo, without any a priori assumptions about the disk's structure. Our method therefore allows us to make detailed predictions regarding stellar populations across the break region. We find that the break is seeded by a drop in star formation density, while the outer exponential is populated almost exclusively by stars that migrated there from the interior. The large extent of radial migration has far-reaching implications for studies ranging from the solar neighborhood to extragalactic stellar populations. I will discuss preliminary results from cosmological simulations as well as observational evidence that lends support to this theory.