The Stellar Initial Mass Function in the Galactic Center

Massive stars define the upper limits of the star formation process, dominate the energetics of their local environs, and significantly affect the chemical evolution of galaxies. Their role in starburst galaxies and the early Universe is likely to be important, but we still do not know the maximum mass that a star can possess, i.e.“the upper mass cutoff.” I will discuss results from a program to measure the upper mass cutoff and IMF slope in the Galactic Center. The results suggest that the IMF in the Galactic center may deviate significantly from the Salpeter value, and that there may be an upper mass cutoff to the initial mass function of ∼150 Msun. 1. Motivating Questions Two simple, yet still unanswered, questions motivate this paper. First, is the stellar initial mass function (IMF) universal? Second, what is the most massive star that can form? These questions are related, as they concern primary output products of the star formation process. The IMF is observed to be roughly constant, within errors, although outliers to the value of the slope do exist. The data at the high mass end are woefully incomplete for determining the upper limit for which the IMF essentially becomes zero, i.e. an upper mass cutoff. There are several properties of stellar clusters that are required for estimating the high mass IMF slope and, in particular, an upper mass cutoff: 1 the associated star formation event must produce a large amount of mass in stars, at least 10 M⊙, 2 the resultant cluster must be young enough, certainly no older than 3 Myr, so that its most massive members are pre-supernovae,