The spatial distributions of HII regions in irregular galaxies

CCD H alpha and V-band images were used to examine the distributions of sta r-forming regions in 34 irregular galaxies, 28 of which are normal Im's and six of which are blue compact dwarf (BCD)/starburst irregulars. The V-band images were used to determine the center, position angle, and inclination of the galaxies. The H alpha images were used to trace the star formation t hrough H II regions. H II region distributions in the plane of the galaxies were compared to turnovers in the rotation curves, the sizes of the galaxi es, and locations relative to stellar bars. The overall symmetry and concen tration of the H II distributions were also determined. The H II regions ar e concentrated toward the inner halves of 88% of the galaxies. Furthermore, most of the H II regions and complexes are located within R-25, the radius at a B surface brightness of 25 mag arcsec(-2), as well as within the part of the galaxy that is rotating as a solid body. Most giant H II regions an d complexes are even more centrally concentrated than the bulk of the H II regions and there is otherwise no preferred location. There are no obvious differences in the distribution of H II regions in BCDs and starburst galax ies relative to that of typical irregulars. However, in one BCD/starburst g alaxy there are H II complexes located well beyond the turnover in the rota tion curve, indicating that not all galaxies with intense star formation ar e unusually centrally concentrated. Finally, the overall distribution of H II regions is symmetrical in most of the galaxies. Some of the irregular ga laxies in our sample have normal rotation curves, while others show no meas urable ordered rotation. Most of the galaxies that do not have measurable r otation have lower star formation rates, while those with measurable rotati on velocities extend to higher star formation rates. In addition, the degre e of central concentration of H II regions is low in the galaxies with no m easurable ordered rotation, and the galaxies with the fastest V-rot,V-max h ave among the highest central concentrations of H II regions.