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We present an objective, non-linear, least-squares algorithm for modelling the observed two-dimensional luminosity distributions in edge-on spiral and lenticular galaxies. The technique has three particular advantages: the entire projected 2D luminosity distribution is fitted; a wide range of combinations of luminosity components can be tested, and an objective criterion is provided which allows one to specify the adequacy of the imposed parametric representation. One may therefore discriminate between the efficacy of different luminosity profiles as a valid representation of an observed galaxy, thereby addressing such questions as whether spiral bulges are adequately described by an r1/4 law, as well as testing the need for multi-component modelling of galaxies (pertinent to identifying evidence for intermediate photometric components). We find that the Sbc galaxy NGC 891 is adequately described by a simple two-component model, although none of the best-fit model combinations contains the standard r1/4 law profile. For NGC 4565, a three-component combination is required, in addition to the ‘box/peanut’ bulge which appears to be an additional independent component of the non-thin disc luminosity at the centre of this galaxy. The bulge components of spiral galaxies are neither all similar, nor are they adequately described by the r1/4 law.
Shaw et al. (Sat,) studied this question.