A morphological type dependence in the μo-log h plane of spiral galaxy disks

We present observational evidence for a galaxy type dependence to the location of a spiral galaxy's disk parameters in the mu (o)-log h plane. With a sample of approximately 40 low surface brightness galaxies (both bulge- and disk-dominated) and approximately 80 high surface brightness galaxies, the early-type disk galaxies (less than or equal to Sc) tend to define a bright envelope in the mu (o)-log h plane, while the late-type (greater than or equal to Scd) 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 modeled with a seeing-convolved Sersic r(1/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 among the high surface brightness galaxies, extends to the low surface brightness galaxies, revealing a continuous range of structural parameters.