SIMBAD references

Using calibrated H-alpha CCD images, we have examined the structure of most of the known H II regions in the irregular galaxy NGC 6822. To search for observaitonal clues to the reasons for the different morphologies, we have examined correlations between several quantitative parameters (peak surface brightness, full-width half-maximum, position, local H I intensity, total emission-line luminosity) and one qualitative one (morphological type). Although many weak correlations exist among these data sets, the only strong bivariate correlation found was between luminosity and size. Multivariate analysis (using principal components analysis) shows that there are no other strong correlations, indicating that the variety displayed in the morphologies of these H II regions is the result of significant differences in the physical parameters that govern them (mass, exciting star or stars, gas density and distribution, dust density and distribution, dynamics, evolutionary state). No simple scaling of parameters can explain the observations.