We derive distance , density and metallicity distribution of the stellar Monoceros Overdensity ( MO ) in the outer Milky Way , based on deep imaging with the Subaru Telescope .
We applied CMD fitting techniques in three stripes at galactic longitudes : l \sim 130 \arcdeg , 150 \arcdeg , 170 \arcdeg ; and galactic latitudes : +15 ^ { \circ } \leq b \leq +25 ^ { \circ } .

The MO appears as a wall of stars at a heliocentric distance of \sim 10.1 \pm 0.5 kpc across the observed longitude range with no distance change .
The MO stars are more metal rich ( [ Fe/H ] \sim - 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 disc model , which predicts a significant drop in density adjacent to the MO that is not seen ; a basic flared disc model , which can give a good match to the density profile but the MO metallicity implies the disc is too metal rich to source the MO stars ; and a tidal stream model , which , from the literature , bracket the distances and densities we derive for the MO , suggesting that a model can be found that would fully fit the MO data .
Further data and modeling will be required to confirm or rule out the MO feature as a stream or as a flaring of the disc .