A Gaseous Group with Unusual Remote Star Formation

We present VLA 21-cm observations of the spiral galaxy ESO 481-G017 to determine the nature of remote star formation traced by an Hii region found 43kpc and ~800kms^-1 from the galaxy center (in projection). ESO 481-G017 is found to have a 120kpc Hi disk with a mass of 1.2×10¹⁰M_solar and UV GALEX images reveal spiral arms extending into the gaseous disk. Two dwarf galaxies with Hi masses close to 10⁸M_solar are detected at distances of ~200kpc from ESO 481-G017 and a Hi cloud with a mass of 6×10⁷M_solar is found near the position and velocity of the remote Hii region. The Hii region is somewhat offset from the Hi cloud spatially and there is no link to ESO 481-G017 or the dwarf galaxies. We consider several scenarios for the origin of the cloud and Hii region and find the most likely is a dwarf galaxy that is undergoing ram pressure stripping. The Hi mass of the cloud and Hα luminosity of the Hii region (10^38.1ergs^-1) are consistent with dwarf galaxy properties, and the stripping can trigger the star formation as well as push the gas away from the stars.