Authors: Alister W. Graham & W.J.G. de Blok
Abstract: We present observational evidence for a galaxy `Type' dependence to the location of a spiral galaxy's disk parameters in the μ0-log(h) plane. With a sample of ~40 Low Surface Brightness galaxies (both bulge- and disk-dominated) and ~80 High Surface Brightness galaxies, the early-type disk galaxies (less than Sc) tend to define a bright envelope in the μ0-log(h) plane, while the late-type (greater than Sc) spiral galaxies have, in general, smaller and fainter disks. Below the defining surface brightness threshold for a Low Surface Brightness galaxy (i.e. more than 1 mag fainter than the 21.65 B-mag arcsec-2 Freeman value), the early-type spiral galaxies have scale-lengths greater than 8-9 kpc, while the late-type spiral galaxies have smaller scale-lengths. All galaxies have been modelled with a seeing-convolved Sérsic r1/n bulge and exponential disk model. We show that the trend of decreasing bulge shape parameter (n) with increasing Hubble type and decreasing bulge-to-disk luminosity ratio, which has been observed amongst the High Surface Brightness galaxies, extends to the Low Surface Brightness galaxies, revealing a continuous range of structural parameters.