Pecular velocities of galaxies in the Leo Spur

Abstract

Hubble Space Telescope Advanced Camera for Surveys has been used to determine accurate distances for the spiral galaxy NGC2683 and 12 other galaxies in a zone of the "local velocity anomaly" from measurements of the luminosities of the brightest red giant branch stars. These galaxies lie in the Leo Spur, the nearest filament beyond our home Local Sheet. The new, accurate distance measurements confirm that galaxies along the Leo Spur are more distant than expected from uniform cosmic expansion, hence have large peculiar velocities toward us. The motions are generally explained by a previously published model that posits that the Local Sheet is descending at 259 km/s toward the south supergalactic pole due to expansion of the Local Void and being attracted at 185 km/s toward the Virgo Cluster. With the standard $Λ$CDM cosmology an empty void expands at 16 km/s/Mpc so a motion of 259 km/s requires the Local Void to be impressively large and empty. Small residuals from the published model can be attributed to an upward push toward the north supergalactic pole by expansion of the Gemini-Leo Void below the Leo Spur. The Leo Spur is sparsely populated but among its constituents there are two associations that contain only dwarf galaxies.