Evidence against a Scale-free Hubble Sequence for Spirals

We investigate recent claims that the Hubble sequence of spiral galaxies is scalefree. Fundamental to this investigation is the fact that within the photometric data of 86 spiral galaxies from de Jong & van der Kruit (1994) from which these claims were made a trend exists between morphological type and bulge profile shape. While late-type spiral bulges are described by an exponential luminosity profile, the early-type spiral bulges are better described by an r1/2 or r1/4 law. Taking the scale-lengths from the best-fitting surface brightness profile models (i.e. either using exponential, r1/2, or r1/4 law profile parameters), we apply a statistical analysis to show that the ratio of re/h varies with Hubble type. Early-type spirals have a larger re/h ratio than late-type spirals in agreement with the classification scheme established by Hubble (1926, 1936). In contrast to this, fitting an exponential profile to the bulges of all spirals results in the mean re/h ratio for the early-type spirals actually being smaller than the mean re/h ratio for the late-type spirals (at the 5σ significance level! using K-band data). Subject headings: galaxies: spiral, galaxies: structure, galaxies: fundamental parameters, galaxies: formation