Inner and outer photometric structure of elliptical galaxies

The Nuker model, when applied to the inner regions of 'core' galaxies, is shown to produce systematic biases in the determination of the core break radii. These can easily be (and often have been, see also Trujillo et al. 2002) over-estimated by more than 100%. Moreover, due to curvature in the outer profiles of early-type galaxies, none of the Nuker model parameters are found to be robust quantities. A new empirical model that simultaneously describes both the inner and outer light-profiles of elliptical galaxies (and bulges in general) is presented. In a sense, it is hybrid of the Nuker model and consists of an inner power-law, a transition region, and an outer Sersic function.