case western reserve university



Clues about Disk Evolution from the Outermost Reaches of Galaxies

Rok Roskar (Washington)

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. We simulate a suite of idealized models representative of galaxy formation through dissipational collapse after the last major merger. 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 on surprisingly circular orbits. The degree of such radial migrations is large and unexpected. I will discuss the theoretical basis for this phenomenon and present observational evidence that lends support to the theory. I will also briefly chart out some far-reaching implications of such migrations for studies ranging from the solar neighborhood to extragalactic stellar populations.