The radial distribution of H II regions in spiral galaxies

We have examined the radial distribution of H II regions in the rectified planes of 37 galaxies. They group themselves into three broad classes: those with continually decreasing density outward, those with oscillating density, and those with doughnut-shaped density distributions. Generally, the second class is made up largely of SB galaxies, and the last is mostly populated by early Hubble types. A correlation is also found with absolute magnitude, which increases along the sequence given above. Most galaxies' outer H II regions distributions show an exponential decrease in density, with a slope that is strongly correlated with Hubble type and absolute magnitude. We also find a correlation between Hubble type and the size of H II region density fluctuations, in the sense that later Hubble types show smaller differences in H II region density.