Theoretical predictions for surface brightness fluctuations and implications for stellar populations of elliptical galaxies

We compute theoretical predictions for surface brightness fluctuations (SBF s) of single-burst stellar populations (SSPs) using models optimized for th is purpose. We present results over a wide range of ages (from 1 to 17 Gyr) and metallicities (from 1/200 to 2.5 times solar) and for a comprehensive set of ground-based and space-based optical and infrared bandpasses. Our mo dels agree well with existing SBF observations of Milky Way globular cluste rs and elliptical galaxies. Our results also provide refined theoretical ca librations and k-corrections that are needed to use SBFs as standard candle s. We suggest that SBF distance measurements can be improved by (1) using a filter around 1 mum to minimize the influence of stellar population variat ions, and (2) using the integrated V-K galaxy color instead of V-I-c to cal ibrate I-band SBF distances. In addition, we show that available SBF observ ations set useful constraints on current population synthesis models, and w e suggest SBF-based tests for future models. The existing SBF data favor pa rticular choices of stellar evolutionary tracks and spectral libraries amon g the several choices allowed by comparisons based on only the integrated p roperties of galaxies. Also, the tightness of the empirical I-band SBF cali bration as a function of V-I-c galaxy color is a useful constraint. It sugg ests that the model uncertainties in the lifetimes of the post-main-sequenc e evolutionary phases are probably less than +/- 50% and that the initial m ass function in elliptical galaxies is probably not much steeper than that in the solar neighborhood. Finally, we analyze the potential of SBFs for pr obing unresolved stellar populations in elliptical galaxies. Since SBFs dep end on the second moment of the stellar luminosity function, they are sensi tive to the brightest giant stars and provide complementary information to commonly used integrated light and spectra. In particular, we find that opt ical/near-infrared SBFs are much more sensitive to the metallicity than the age of a stellar population. Therefore, in combination with age-sensitive observables, SBF magnitudes and colors are a valuable complement to metal-l ine indices to break the age/metallicity degeneracy in elliptical galaxy st udies. Out preliminary results suggest that the most luminous stellar popul ations of bright galaxies in nearby clusters have roughly solar metalliciti es and about a factor of 3 spread in age.