2. Background

This chapter gives background information necessary for the subsequent chapters. Section  introduces the observable quantities which are derived from the data in Chapter -, and on which the analysis (Chapter ) is based. Section  introduces the Fundamental Plane (FP), and explores the physics underlying the relation. Section  describes stellar population synthesis models. These models predict observable quantities like the mass-to-light ratios and line strengths, and can be used to infer mean ages and metallicities from the observations. They can also be used to interpret the found relations between the observable quantities in terms of variations in mean age or metallicity.