No Excess of RR Lyrae Stars in the Canis Major Overdensity

Abstract

Our multi-epoch survey of ~20 sq. deg. of the Canis Major overdensity has detected only 10 RR Lyrae stars (RRLS). We show that this number is consistent with the number expected from the Galactic halo and thick disk populations alone, leaving no excess that can be attributed to the dwarf spheroidal (dSph) galaxy that some authors have proposed as the origin of the CMa overdensity. If this galaxy resembles the dSph satellites of the Milky Way and of M31 and has the putative Mv~-14.5, our survey should have detected several tens of RRLS. Even if Mv<-12, the expected excess is >10, which is not observed. Either the old stellar population of this galaxy has unique properties or, as others have argued before, the CMa overdensity is produced by the thin and thick disk and spiral arm populations of the Milky Way and not by a collision with a dSph satellite galaxy.

35 pages, 9 figures, 5 tables. Accepted for publication at the Astronomical Journal

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• Near-Infrared Variability Study of the Central 2.3 arcmin x 2.3 arcmin of the Galactic Centre II. Identification of RR Lyrae Stars in the Milky Way Nuclear Star Cluster
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• APOGEE discovery of a chemically atypical star disrupted from NGC 6723 and captured by the Milky Way bulge
• An updated detailed characterization of planes of satellites in the MW and M31
• Identification of RR Lyrae stars in multiband, sparsely-sampled data from the Dark Energy Survey using template fitting and Random Forest classification
• STREGA: STRucture and Evolution of the GAlaxy. I. Survey Overview and First Results
• On the Origin of the Monoceros Ring - I: Kinematics, proper motions, and the nature of the progenitor
• Globular Clusters in the Outer Halo of M31
• A Megacam Survey of Outer Halo Satellites. IV. Two foreground populations possibly associated with the Monoceros substructure in the direction of NGC2419 and Koposov2
• A revised view of the Canis Major stellar overdensity with DECam and Gaia: new evidence of a stellar warp of blue stars