Monoceros Overdensity deep imaging with Subaru

We applied color-magnitude diagram fitting techniques in three stripes at galactic longitudes, l~130{deg}, 150{deg}, 170{deg}, and galactic latitudes, +15{deg}<=b<=+25{deg}. The MO appears as a wall of stars at a heliocentric distance of ~10.1+/-0.5kpc across the observed longitude range with no distance change.

The MO stars are more metal-rich ([Fe/H]~-1.0) than the nearby stars at the same latitude. These data are used to test three different models for the origin of the MO: a perturbed disk model, which predicts a significant drop in density adjacent to the MO that is not seen; a basic flared disk model, which can give a good match to the density profile but the MO metallicity implies the disk is too metal-rich to source the MO stars; and a tidal stream model, which, from the literature, brackets the distances and densities we derive for the MO, suggesting that a model can be found that would fully fit the MO data.