THE DEPENDENCE OF THE BRIGHTNESS FLUCTUATION DISTANCE INDICATOR ON STELLAR POPULATION AGE AND METALLICITY

We describe how the extragalactic distance indicator LBAR depends on s tellar population age, metallicity, and IMF, assuming single-burst age s between 5 and 17 Gyr and metallicities between -0.5 and +0.5 dex. We consider Johnson/Cousins BVR(C)I(C)JHKLL'M passbands. We find that (1 ) LBAR is insensitive to changes in IMF, (2) LBAR can be reliably cali brated against colors or spectral indices, due to the similarity of th e effects of age and metallicity on the stellar populations, (3) the c alibration presented here may already give distances good to 10% for a n isolated galaxy measured in one fluctuation passband and one color o r spectral index, not including observational error, and (4) our theor etical results are consistent with the distance of M32 and with the la test empirical IBAR calibration and require no empirical corrections. We summarize our results by giving polynomial calibrations for MBAR as functions of integrated Mg2, V-I, and J-K.