Absolute Proper Motion of the Canis Major Dwarf Galaxy Candidate

We have measured the absolute proper motion of the candidate Canis Major dwarf galaxy (CMa), at ( l , b ) =(240°, -8°). Likely main-sequence stars in CMa have been selected from a region in the color-magnitude diagram that has very little contamination from known Milky Way components. We obtain μ l cos b = -1.47 ± 0.37 and μ b = -1.07 ± 0.38 mas yr -1 , on the International Celestial Reference System by means of Hipparcos stars. Together with the radial velocity of 109 km s -1 and the assumed distance of 8 kpc, these results imply a space motion of (Π, Θ, W ) = (-5 ± 12, 188 ± 10, -49 ± 15) km s -1 . While CMa has in-plane rotation similar to the mean of thick-disk stars, it shows significant (3 σ) motion perpendicular to the disk and differs even more (7 σ) from that expected for the Galactic warp. The W -velocity lends support to the argument that the CMa overdensity is part of a satellite-galaxy remnant.