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1. Introduction

In this chapter we will discuss the results obtained from the fitting of mass models to the rotation curves, described in chapter 6. We will compare these results with data on other physical quantities, and with the morphological types. Such a task is not easy, however, most of the physical quantities of interest can only be derived by adopting theoretical models: The results presented in chapter 6 depend on the adopted mass models and the results on the radial distribution of light, for example, depend on assumptions concerning the absorption correction. In fact, each of the comparisons we want to make requires study of the assumptions underlying the determination of the quantities of interest. Insufficient time was available to make an exhaustive study of all these problems. We therefore present an abbreviated study of the main quantities of interest, but we intend to work out several aspects at a later stage.

The structure of this chapter is as follows: In section 2 we discuss the problem of the mass and size of galaxies. In section 3 we present data on the mass-to-light ratio of various galaxies and the variation of this ratio within galaxies. In section 4 we discuss the radial variation of total mass to HI gas mass surface density in a number of galaxies, and in section 5 we discuss the radial extent of the HI distribution. Finally, in section 6 we treat the relationship of the physical quantities discussed in this thesis with morphological type.