The Initial Mass Function of the Galactic Bulge Down to ~ 0.15 M ⊙

Abstract

We present a luminosity function (LF) for lower main sequence stars in the Galactic bulge near (1, b) _ (0°, —6°) to M,, — 9.3. This LF is derived from HST+NICMOS observations of a region of 221.’5 x 221’5, with the F11OW and F160W filters. Our derived mass function extends to 0.15M ⊙with a power law slope of a = —1.33 ± 0.07. Although shallower than the Salpeter one, this IMF is steeper than that recently found for the Galactic disk (a = —0.8 and a = —0.54 from the data of Reid & Gizis,1997,and Gould et al. 1997, respectively, in the same mass interval), but is virtually identical to the disk IMF derived by Kroupa et al. (1993). The bulge IMF is also quite similar to the mass functions derived for those globular clusters which are believed to have experienced little or no dynamical evolutionKeywordsGlobular ClusterLuminosity FunctionGalactic DiskInitial Mass FunctionDistance ModulusThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.