On the light-profiles of spiral galaxy bulges and the hubble sequence for spirals

Recent studies have claimed that the Hubble sequence of late-type spirals, and spirals in general, is scale-free. Within the photometric data used in these works, a trend exists between morphological type and bulge profile shape such that late-type spiral bulges are described by an exponential luminosity profile, where-as the early-type spiral bulges are better described by an r 1/2 or r 1/4 law. The universal application of an exponential light-profile to the disk and bulge of all spiral galaxies is not justified. Taking structural parameters from exponential disk models and the best-fitting rl/n bulge models (with n = 1, 2 or 4), the mean effective-bulge-radius to disk scale-length ratio (re/h) increases at the 3