The Distance and Metallicity of the Newly Discovered, Nearby Irregular Galaxy HIZSS3

Abstract

HIZSS3 is an H I source in the Zone of Avoidance. Its radio characteristics are consistent with it being nearby (~ 1.8 Mpc) low-mass dwarf irregular (dIm) galaxy. It contains a modest H II region, but its stellar population has not been resolved by optical observations. MMT spectra of the H II region are used to derive the line-of-sight extinction (E(B-V) = 1.41 +/- 0.04) and gas metallicity (log O/H + 12 ~ 7.8). ESO VLT near-IR images clearly reveal a resolved stellar population. Narrow-band Pbeta images of the H II region are used in combination with previously published Halpha 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. Based on 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 (TRGB) 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 HIZSS3 is a newly discovered low-mass dIm lurking behind the Milky Way in the outskirts of the Local Group.