THE INFLUENCE OF STELLAR POPULATIONS ON ELLIPTICAL GALAXY DISTANCE ESTIMATES

摘要

Simple models are used to gauge the effects of stellar populations on elliptical galaxy distance estimates based on the fundamental plane (FP). The models are characterized by varying age, the slope of the initial mass function, and metallicity. Varying these quantities within astrophysically plausible limits can systematically affect distance estimates by factors of up to several. Two nearby examples where this occurs are presented. Coupled with the thinness of the FP of the Coma Cluster, the models constrain the spread in ages of the Coma elliptical galaxies to be ≤ 1.5 Gyr and the spread in initial mass function slope to be approximately 0.7 ≤ x ≤ 1.1. It is argued that if a difference in mean age exists between ellipticals in the Virgo and Coma clusters (Bower et al. 1990), then the Coma-Virgo relative distance based on the FP has been overestimated; however, the modeling is too crude to estimate the size of the effect reliably. The results also predict that FP distance estimates at redshifts of ～0.5 or greater will yield spurious peculiar velocities of several times 10~4 km s~(-1) unless corrected for luminosity evolution. The D-σ relation in the Coma Cluster has 15%-28% less scatter in the I band and nearly a factor of 2 less in the K band, suggesting that distance estimates to elliptical galaxies based on red and infrared photometry are more accurate than those derived from B-band photometry. Stellar population effects and extinction probably both contribute to this effect.