Stellar Populations of Elliptical Galaxies from Surface Brightness Fluctuations

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We are using optical/IR surface brightness fluctuations (SBFs) to validate the latest stellar population synthesis models and to understand the stellar populations of ellipticals. Integrated light and spectra measure only the first moment of the stellar luminosity function (Σnᵢ * Lᵢ). Since SBFs also depend on the second moment (Σnᵢ * Lᵢ²), they provide novel information, in particular about the reddest, most luminous RGB and AGB stars, which are the most difficult stars to model. SBFs can also provide useful new constraints on the age/metallicity of unresolved stellar populations in ellipticals. Finally, developing accurate stellar population models benefits several aspects of SBF distance measurements to galaxies.