Theoretical Predictions for Surface Brightness Fluctuations and Implications for Stellar Populations of Elliptical Galaxies

We compute theoretical predictions for surface brightness fluctuations (SBFs) of single-burst stellar populations (SSPs) using models optimized for this 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 models agree well with existing SBF observations of Milky Way globular clusters and elliptical galaxies. Our results provide refined theoretical calibrations and k-corrections that are needed to use SBFs as standard candles. We suggest that SBF distance measurements can be improved by (1) using a filter around 1 μm to minimize the influence of stellar population variations, and (2) using the integrated V −K galaxy color instead of V − Ic to calibrate I-band SBF distances. We show that available SBF observations set useful constraints on current population synthesis models, and we suggest SBF-based tests for future models. The existing SBF data favor particular choices of stellar evolutionary tracks and spectral libraries among the several choices allowed by comparisons based on only the integrated properties of galaxies. Also, the tightness of the empirical I-band SBF calibration as a function of V − Ic galaxy color is a useful constraint. It suggests that the model uncertainties in the lifetimes of the post-main sequence evolutionary phases are probably less than ±50% and that the initial mass function in elliptical galaxies is probably not much steeper than that in the solar neighborhood. Finally, we analyze the potential of SBFs for probing unresolved stellar populations in elliptical galaxies. Since SBFs depend on the second moment of the stellar luminosity function, they are sensitive to the brightest giant stars and provide complementary information to commonly-used integrated light and spectra. In particular, we find that optical/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-line indices to break the age/metallicity degeneracy in elliptical galaxy studies. Our preliminary results suggest that the most luminous stellar populations of bright galaxies in nearby clusters have roughly solar metallicites and about a factor of three spread in age. Subject headings: cosmology: distance scale — Galaxy: globular clusters — galaxies: elliptical and lenticular, stellar content, formation — stars: late-type, AGB and post-AGB