An ice-berg scenario for late-type spiral galaxy bulges.

Fitting exponential profiles to the bulges of the early-type spiral galaxies from de Jong & van der Kruit (1994) under-estimates their sizes at the 2-3 sigma significance level. Allowing for the range of structural shapes which these bulges possess - through fitting an r1/n profile - the mean effective bulge radius to disk scale-length ratio, re/h, is larger for the early-type spirals than the late-type spirals at the 1.5-2 sigma level in the optical passbands, and only the 1 sigma level in the K-band. The bulge-to-disk size ratio is therefore not a useful parameter for determining morphological type in spirals. However, the central galaxy (bulge+disk) surface brightness minus the central disk surface brightness is significantly (>3 sigma) brighter for the early-type spirals than the late-type spirals. Similarly, the `normalised' radius at which the bulge and disk light contribute equally is significantly larger for the early-type spirals, and we propose these parameters to help quantify the Hubble sequence for spirals. If the mean bulge-to-disk size ratio is indeed the same for early- and late-type spirals, it implies that the bulges of late-type spirals must be relatively submerged in the disk when compared to the bulges of early-type spirals.