The Distance and Metallicity of the Newly Discovered, Nearby Irregular Galaxy HIZSS 3

HIZSS3 is an H I source in the Zone of Avoidance. Its radio characteristicsare 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 notbeen resolved by optical observations. MMT spectra of the H II region are usedto derive the line-of-sight extinction (E(B-V) = 1.41 +/- 0.04) and gasmetallicity (log O/H + 12 ~ 7.8). ESO VLT near-IR images clearly reveal aresolved stellar population. Narrow-band Pbeta images of the H II region areused in combination with previously published Halpha data to obtain anindependent line-of-sight extinction estimate: E(B-V) = 1.32 +/- 0.04. Theadopted foreground extinction is E(B-V) = 1.36 +/- 0.06. Based on the K-bandluminosity function and K,J-K color-magnitude diagram, the apparent magnitudeand color of the tip of the red-giant branch (TRGB) are derived. In turn, theseparameters are combined with the adopted foreground extinction to estimate thedistance (1.69 +/- 0.07 Mpc) and mean red giant branch metallicity ([Fe/H] =-0.5 +/- 0.1). As an ensemble, these new observations significantly strengthenthe conclusion that HIZSS3 is a newly discovered low-mass dIm lurking behindthe Milky Way in the outskirts of the Local Group.Comment: Accepted, scheduled for ApJ, 10 Apr 05, V623 ; 14 page