Astron. J., 119, 1145-1156 (2000/March-0)
The spatial distributions of H II regions in irregular galaxies.
ROYE E.W. and HUNTER D.A.
Abstract (from CDS):
CCD Hα and V-band images were used to examine the distributions of star-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 Hα images were used to trace the star formation through 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 galaxies, and locations relative to stellar bars. The overall symmetry and concentration of the H II distributions were also determined. The H II regions are concentrated toward the inner halves of 88% of the galaxies. Furthermore, most of the H II regions and complexes are located within R25, 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 and 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 galaxies relative to that of typical irregulars. However, in one BCD/starburst galaxy there are H II complexes located well beyond the turnover in the rotation curve, indicating that not all galaxies with intense star formation are unusually centrally concentrated. Finally, the overall distribution of H II regions is symmetrical in most of the galaxies. Some of the irregular galaxies in our sample have normal rotation curves, while others show no measurable ordered rotation. Most of the galaxies that do not have measurable rotation have lower star formation rates, while those with measurable rotation velocities extend to higher star formation rates. In addition, the degree of central concentration of H II regions is low in the galaxies with no measurable ordered rotation, and the galaxies with the fastest Vrot,max have among the highest central concentrations of H II regions.
Galaxies: Irregular - ISM: H II Regions - Stars: Formation
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