The Arecibo Galaxy Environment Survey - VIII. Discovery of an isolated dwarf galaxy in the Local Volume.

The Arecibo Galaxy Environment Survey has detected a nearby H I source at a heliocentric velocity of +363 km s^-1. The object was detected through its neutral hydrogen emission and has an obvious possible optical counterpart in Sloan Digital Sky Survey data (though it does not have an optical redshift measurement). We discuss three possible scenarios for the object: (1) it is within the Local Group, in which case its H I properties are comparable with recently discovered ultracompact high-velocity clouds; (2) it is just behind the Local Group, in which case its optical characteristics are similar to the newly discovered Leo P galaxy; (3) it is a blue compact dwarf galaxy within the local volume but not associated with the Local Group. We find the third possibility to be the most likely, based on distance estimates from the Tully-Fisher relation and its velocity relative to the Local Group.