New optical and near-infrared surface brightness fluctuation models: A primary distance indicator ranging from globular clusters to distant galaxies?

We present new theoretical models for surface brightness fluctuations (SBFs) both for optical and near-infrared bands in standard ground-based and Hubble Space Telescope filter systems. Simple stellar population simulations are adopted. Models cover the age and metallicity ranges from 5 to 15 Gyr and from Z=0.0001 to Z=0.04, respectively. Effects due to variation of the initial mass function and the stellar color-temperature relation are explored. Particular attention is devoted to very bright stars in the color-magnitude diagram and to investigating the effects of mass loss along the red giant branch (RGB) and the asymptotic giant branch (AGB). It is found that U- and B-band SBF amplitudes are powerful diagnostics for the morphology of the horizontal branch and the post-AGB star population. We point out that a careful treatment of the mass-loss process along the RGB and AGB is fundamental to determining reliable SBF evaluations. The SBF measurements are used to place robust constraints on the evolution of AGB stars, suggesting that the mass-loss activity of AGB stars should be twice as efficient as that of RGB stars. Our models are able to reproduce the absolute SBF magnitudes of Galactic globular clusters and of galaxies and their integrated colors. New calibrations of absolute SBF magnitude in V, R, I, and K photometric filters are provided, which appear reliable enough to directly gauge distances, bypassing other distance indicators. The SBF technique is also used as a stellar population tracer to derive the age and metallicity of a selected sample of galaxies of known distances. Finally, SBF color versus integrated color diagrams are proposed as particularly useful in removing the well-known age-metallicity degeneracy affecting our knowledge of remote stellar systems.