On the neutral gas content and environment of NGC 3109 and the Antlia dwarf galaxy

As part of a continuing survey of nearby galaxies, we have mapped the neutral gas content of the low surface brightness Magellanic-type galaxy NGC 3109 and its environment, including the Antlia dwarf galaxy, at unprecedented velocity resolution and brightness sensitivity. The H I mass of NGC 3109 is measured to be 3.8 +/- 0.5 x 10(8) M-.. A substantial warp in the disk of NGC 3109 is detected in the H I emission image in the form of an extended low surface brightness feature. We report a positive detection in H I of the nearby Antlia dwarf galaxy and measure its total neutral gas mass to be 6.8 +/- 1.4 x 10(5) M-.. We show the warp in NGC 3109 to lie at exactly the same radial velocity as the gas in the Antlia dwarf galaxy and speculate that Antlia disturbed the disk of NGC 3109 during a mild encounter similar to1 Gyr in the past. H I data for a further eight galaxies detected in the background are presented.