A Neighboring Dwarf Irregular Galaxy Hidden by the Milky Way

We have obtained VLA and optical follow-up observations of the low-velocity H I source HIZSS 3 discovered by Henning et al. 2000 and Rivers 2000 in a survey for nearby galaxies hidden by the disk of the Milky Way. Its radio characteristics are consistent with this being a nearby (∼ 1.8 Mpc) low-mass dwarf irregular galaxy (dIm). Our optical imaging failed to reveal a resolved stellar population, but did detect an extended Hα emission region. The location of the Hα source is coincident with a partially-resolved H I cloud in the 21-cm map. Spectroscopy confirms that the Hα source has a similar radial velocity to that of the H I emission at this location, and thus we have identified an optical counterpart. The Hα emission (100 pc in diameter and with a luminosity of 1.4 × 10 ergs s) is characteristic of a single H II region containing a modest population of OB stars. The galaxy’s radial velocity and distance from the solar apex suggests that it is not a Local Group member, although a more accurate distance is needed to be certain. The properties of HIZSS 3 are comparable to those of GR 8, a nearby dIm with a modest amount of current star formation. Further observations are needed to characterize its stellar population, determine the chemical abundances, and obtain a more reliable distance estimate. Subject headings: galaxies: irregular – Local Group