Constraints on the Stellar Mass Function from Stellar Dynamics at the Galactic Center

Abstract

We consider the dynamical evolution of a disk of stars orbiting a central black hole. In particular, we focus on the effect of the stellar mass function on the evolution of the disk, using both analytic arguments and numerical simulations. We apply our model to the ring of massive stars at ~0.1pc from the Galactic Center, assuming that the stars formed in a cold, circular disk, and find that our model requires the presence of a significant population of massive (>100Msun) stars in order to explain the the observed eccentricities of 0.2-0.3. Moreover, in order to limit the damping of the heavier stars' eccentricities, we also require fewer low-mass stars than expected from a Salpeter mass function, giving strong evidence for a significantly ``top-heavy'' mass function in the rings of stars seen near to the Galactic Center. We also note that the maximum possible eccentricities attainable from circular initial conditions at ages of <10Myr are around 0.4-0.5, and suggest that any rings of stars found with higher eccentricities were probably not formed from circular disks.