| Abstract | HIZSS 3 is an H I source in the Zone of Avoidance. Its radio characteristics are consistent with it being a previously unknown, nearby (~1.8 Mpc), low-mass dwarf irregular (dIrr) galaxy. Optical observations have shown that it contains a modest H II region, but they failed to reveal a resolved stellar population. New spectroscopic observations of the H II region obtained at the MMT Observatory are presented here. They are used to derive the line-of-sight extinction [E(B-V)=1.41+/-0.04] and gas metallicity (logO/H+12~7.8) of the H II region. New near-IR imaging observations obtained at the ESO Very Large Telescope are also presented here. These images clearly reveal the resolved stellar population of HIZSS 3 for the first time. Narrowband Paβ images of the H II region are used in combination with previously published Hα data to obtain an independent line-of-sight extinction estimate: E(B-V)=1.32+/-0.04. The adopted foreground extinction is E(B-V)=1.36+/-0.06. Using the K-band luminosity function and K,J-K color-magnitude diagram, the apparent magnitude and color of the tip of the red giant branch are derived. In turn, these parameters are combined with the adopted foreground extinction to estimate the distance (1.69+/-0.07 Mpc) and mean red giant branch metallicity ([Fe/H]=-0.5+/-0.1). As an ensemble, these new observations significantly strengthen the conclusion that HIZSS 3 is a newly discovered low-mass dIrr galaxy lurking behind the Milky Way in the outskirts of the Local Group. The optical spectroscopic observations reported here were obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona. The near-IR imaging observations reported here were collected at the European Southern Observatory, Cerro Paranal, Chile, within observing program 271.B-5047. |
