The H alpha Galaxy Survey VII. The spatial distribution of star
  formation within disks and bulges
  We analyse the current build-up of stellar mass within the disks and bulges
of nearby galaxies through a comparison of the spatial distributions of forming
and old stellar populations. H alpha and R-band imaging are used to determine
the distributions of young and old stellar populations in 313 S0a - Im field
galaxies out to 40 Mpc. Concentration indices and mean normalised light
profiles are calculated as a function of galaxy type and bar classification.
The mean profiles and concentration indices show a strong and smooth dependence
on galaxy type. Apart from a central deficit due to bulge/bar light in some
galaxy types, mean H alpha and R-band profiles are very similar. Mean profiles
within a given type are remarkably constant even given wide ranges in galaxy
luminosity and size. SBc, SBbc and particularly SBb galaxies have profiles that
are markedly different from those of unbarred galaxies. H alpha emission from
SBb galaxies is studied in detail; virtually all show resolved central
components and concentrations of star formation at or just outside the bar-end
radius. In these galaxies, star formation has the same radial distribution as
R-band light, i.e. stellar mass is building at approximately constant
morphology, with no strong evidence for outer truncation or inside-out disk
formation. (Abridged.)
