The properties of the Antlia dwarf galaxy

We present a deep (I,V-I) color-magnitude diagram (CMD) for the recently re-discovered nearby dwarf galaxy located in the constellation of Antlia. Our photometry reveals a relatively steep red giant branch (RGB) extending from I approximate to 21.5 to the faint limit of I approximate to 25.5. Analysis of the CMD shows that Antlia contains young, intermediate-age, and old stellar populations, Furthermore, the young population is only present inside approximate to 0.5 arcmin from the center of Antlia. The tip of the first ascent RGB is well-defined and is used to estimate a distance, but it shows a hint of fine structure indicative of extinction effects due to dust within Antlia itself. This is consistent with the fact that extant observations in the 21 cm line of neutral hydrogen indicate the presence of significant amounts of H I in Antlia. However, our observations do not allow an unequivocal statement to be made about the interstellar dust content of Antlia. If Antlia contains non-negligible amounts of dust, then we estimate its distance to be 1.24+/-0.10 Mpc ((I-M-I)(0)=25.47 +/-0.13) and its mean metallicity is [[Fe/H]]= -2.41 degrees +/- 0.18. In contrast, if Antlia contains little or no dust, then its distance is 1.33+/-0.10 Mpc [(I-M-I)(0)=25.62+/+0.12] and its metallicity is [[Fe/H]]=-1.90 +/-0.13. If the latter abundance is adopted, then Antlia lies squarely on the absolute magnitude versus mean metallicity relation for dwarf spheroidal/elliptical galaxies. However, if one assumes that Antlia contains significant amounts of dust, then its metallicity places it at the extreme metal-poor end of dwarf galaxies. (C) 1997 The American Astronomical Society. [S0004-6256(97)03012-4].