The use of giant H2 region diameters to measure distances to late-type spiral galaxies were critically examined. Sensitometrically calibrated H alpha image tube plates and photoelectric H alpha fluxes were obtained for the largest H2 regions in 40 of the galaxies. These data were used to produce isophotal maps for each nebula of interest, so that their structure could be studied directly, and the published diameters could be tested. Many of the nebulae studied, especially those located in luminous spiral galaxies, were found to possess rather ill-defined outer envelopes of emission, caused either by their intrinsic physical structure or by confusion with neighboring nebulosities and background disk emission.
- Pub Date:
- Physics: Astronomy and Astrophysics;
- Distance Measuring Equipment;
- H Ii Regions;
- Spiral Galaxies;
- Dimensional Analysis;
- Hubble Constant;