Abstract
Surface brightness fluctuations (SBFs) are already a very powerful tool for deriving cosmological distances. However, their promise as diagnostics of unresolved stellar populations has not yet been fulfilled. Here, we present an ongoing project to mine the 2MASS database with exactly that purpose. This work should help 1) explain the observed dispersion of measured SBFs in nearby galaxy clusters; 2) calibrate the stellar population synthesis models that are used, in combination with observational data, to derive cosmological distances; and 3) expand the capabilities of the largest telescopes, like the GTC, to study very distant stellar populations.
