Physical conditions in Giant Extragalactic H II regions

Giant Extragalactic H II Regions (GEHRs) in nearby galaxies were observed at both radio and optical wavelengths. Narrow band optical imaging, large and small aperature optical spectrophotometry, radio continuum imaging at lambda 6 cm and lambda21 cm, and lambda21 cm H I spectral line mapping were employed to investigate the point to point variations of the physical conditions within and surrounding the GEHRs. Measurement of reddening and extinction were found to be strongly dependent on resolution. Variations in extinction as measured by the optical method were not found to correlate with those measured with the optical-radio method. In at least one case this was due to the presence of a nonthermal radio continuum source. Significant differences in optical line strength ratios exist between different points in a single GEHR. These differences point to variations of the physical conditions within the GEHR. The results of standard abundance analysis techniques are therefore dependent on the size and position of the observing aperture