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

• Published in: The Astrophysical journal 2005-04, Vol.623 (1), p.148-158
• Main Authors: Silva, David R, Massey, Philip, DeGioia-Eastwood, Kathleen, Henning, P. A
• Format: Article
• Language: English
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/428341

HIZSS 3 is an H I source in the Zone of Avoidance. Its radio characteristics are consistent with it being a previously unknown, nearby ( similar to 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 plus or minus 0.04] and gas metallicity (log O/H + 12 similar to 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 Pa beta images of the H II region are used in combination with previously published H alpha data to obtain an independent line-of-sight extinction estimate: E(B - V) = 1.32 plus or minus 0.04. The adopted foreground extinction is E(B - V) = 1.36 plus or minus 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 plus or minus 0.07 Mpc) and mean red giant branch metallicity ([Fe/H] = -0.5 plus or minus 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.