A DEEP VIEW OF THE MONOCEROS RING IN THE ANTICENTER DIRECTION: CLUES OF ITS EXTRA-GALACTIC ORIGIN

We present the results of deep imaging obtained at the Canada-France-Hawaii Telescope with MegaCam in the anticenter direction at two different heights above the Galactic disk. We detect the presence of the Monoceros ring in both fields as a conspicuous and narrow main-sequence feature which dominates star counts over a large portion of the color-magnitude diagram down to g' ~ 24. The comparison of the morphology and density of this feature with a large variety of Galactic models excludes the possibility that it can be due to a flare of the Galactic disk, supporting an extra-Galactic origin for this ring-like structure.