A MORPHOLOGICAL-TYPE DEPENDENCE IN THE μ0–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 μ0–log h plane. With a sample of ∼40 Low Surface Brightness galaxies (both bulgeand disk-dominated) and ∼80 High Surface Brightness galaxies, the early-type disk galaxies (≤Sc) tend to define a bright envelope in the μ0–logh plane, while the late-type (≥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 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 r 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. Subject headings: galaxies: fundamental parameters (scale-lengths, surface brightness, bulge-to-disk ratio), galaxies: kinematics and dynamics, galaxies: photometry, galaxies: spiral, galaxies: structure