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 fluctuation (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)(0) 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. for galaxies with E(B-V) greater than or similar to0.2 mag appear to be overestimated by 5-10 per cent, but we do not find significant evidence for large-scale dipole errors in the extinction map. In comparison with 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 alpha -elements in luminous early-type galaxies. We confirm a tight relation between stellar velocity dispersion sigma and the SBF 'fluctuation count' parameter (N) over bar, which is a luminosity-weighted measure of the total number of stars in a galaxy. The correlation between (N) over bar and sigma is even tighter than that between Mg-2 and sigma. 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 on to the SMAC system. The data are used in a forthcoming paper, which compares the distances derived from the FP and SBF methods.