Surface Brightness Distributions in Two Edge-On Spiral Galaxies

Abstract

Of considerable importance to modelling the formation and early evolution of galaxies is the relationship between the spheroids of spirals and SO’s, and those of ellipticals. In this context, the isolation of a thick disc in our own Galaxy (Gilmore et al. (1985)) and in other spirals (van der Kruit (1984); herafter vdK) — aside from their initial discovery in SO’s by Burstein (1979) — has added significance because the luminosity profiles of several spirals seem to be dominated by this component over considerable ranges of galactocentric distance (R) and height (Z). On the other hand, “elliptical-like” spheroids, generally characterised by the de Vaucouleurs r1/4 law, seem to be barely detectable in many galaxies in complete contradiction to our preconception that this model adequately describes all forms of galaxian spheroids.