A Synthesis of Data from Fundamental Plane and Surface Brightness Fluctuation Surveys
We perform a series of comparisons between distance-independent photometric and spectroscopic properties used in the surface brightness fluctuations (SBF) and fundamental plane (FP) methods of early-type galaxy distance estimation. The data are taken from two recent surveys: the SBF Survey of Galaxy Distances and the Streaming Motions of Abell Clusters (SMAC) FP survey. We derive a relation between V-I colour and Mg_2 index using nearly 200 galaxies and discuss implications for Galactic extinction estimates and early-type galaxy stellar populations. We find that the reddenings from Schlegel et al (1998) for galaxies with $E(B{-}V) \gta 0.2$ mag appear to be overestimated by 5--10%, but we do not find significant evidence for large-scale dipole errors in the extinction map. In comparison to stellar population models having solar elemental abundance ratios, the galaxies in our sample are generally too blue at a given Mg_2; we ascribe this to the well-known enhancement of the $α$-elements in luminous early-type galaxies. We confirm a tight relation between stellar velocity dispersion $σ$ and the SBF `fluctuation count' parameter \Nbar, which is a luminosity-weighted measure of the total number of stars in a galaxy. The correlation between \Nbar and $σ$ is even tighter than that between Mg_2 and $σ$. Finally, we derive FP photometric parameters for 280 galaxies from the SBF survey data set. Comparisons with external sources allow us to estimate the errors on these parameters and derive the correction necessary to bring them onto the SMAC system. The data are used in a companion paper which compares the distances derived from the FP and SBF methods.