The spatially resolved mass function of the globular cluster M22

Hubble Space Telescope imaging of M22 has allowed, for the first time, a detailed and uniform mapping of mass segregation in a globular cluster. Luminosity and mass functions from the turnoff down to the mid to lower main sequence are presented for M22 in annular bins from the center of the cluster out to five core radii. Within the core, a significant enhancement is seen in the proportion of 0.5-0.8 M-circle dot stars compared with their numbers outside the core. Numerical modeling of the spatial mass spectrum of M22 shows that the observed degree of mass segregation can be accounted for by relaxation processes within the cluster. The global cluster mass function for M22 is flatter than the Salpeter initial mass function and cannot be represented by a single power law.