THE FORMATION OF KILOPARSEC-SCALE H i HOLES IN DWARF GALAXIES

The origin of kpc-scale holes in the atomic hydrogen (H i) distributions of some nearby dwarf irregular galaxies presents an intriguing problem. Star formation histories (SFHs) derived from resolved stars give us the unique opportunity to study past star-forming events that may have helped shape the currently visible Hi distribution. Our sample of five nearby dwarf irregular galaxies spans over an order of magnitude in both total Hi mass and absolute B-band magnitude and is at the low-mass end of previously studied systems. We use Very Large Array Hi line data to estimate the energy required to create the centrally dominant hole in each galaxy. We compare this energy estimate to the past energy released by the underlying stellar populations computed from SFHs derived from data taken with the Hubble Space Telescope. The inferred integrated stellar energy released within the characteristic ages exceeds our energy estimates for creating the holes in all cases, assuming expected efficiencies. Therefore, it appears that stellar feedback provides sufficient energy to produce the observed holes. However, we find no obvious signature of single star-forming events responsible for the observed structures when comparing the global SFHs of each galaxy in our sample to each other or to those of dwarf irregular galaxies reported in the literature. We also fail to find evidence of a central star cluster in FUV or Hα imaging. We conclude that large Hi holes are likely formed from multiple generations of star formation and only under suitable interstellar medium conditions.

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