4 Surface Brightness Distribution

As explained in Section 3, the two-dimensional surface brightness distribution of a galaxy is usually analysed so as to produce a one-dimensional radial profile. It turns out that the different physical components of galaxies have characteristic radial profiles, so that it is possible to model the radial profiles of different classes of galaxies as sums of different components.

Following [Binney and Merrifield(1998)], as far as surface brighness radial profiles are concerned, we shall here distinguish only two classes of typical galaxies, namely the elliptical galaxies (E) and disk Galaxies (D), where the latter class include spirals and lenticulars. While elliptical galaxies will be modelled as made of a bulge component only, disk galaxies will be considered as the combination of a bulge and a disk component. In both cases, galaxy images are assumed circularly symmetric. Note that all data and modelled numerical values are given in the $I$ band, but that the subsript $I$ will be here dropped for convenience from most formulae. Note also that the derivation of the mathematical results and the description of the notation used in the following are given in the Appendix.