A large-scale extinction map of the Galactic Anticentre from 2MASS

International audienceWe present a 127 × 63-deg2 extinction map of the Anticentre of the Galaxy, based on and colour excess maps from the Two-Micron All-Sky Survey. This 8001-deg2 map with a resolution of 4 arcmin is provided as online material. The colour excess ratio / is used to determine the power-law index of the reddening law (β) for individual regions contained in the area (e.g. Orion, Perseus, Taurus, Auriga, Monoceros, Camelopardalis, Cassiopeia). On average we find a dominant value of β = 1.8 +/- 0.2 for the individual clouds, in agreement with the canonical value for the interstellar medium. We also show that there is an internal scatter of β values in these regions, and that in some areas more than one dominant β values are present. This indicates large-scale variations in the dust properties. The analysis of the AV values within individual regions shows a change in the slope of the column density distribution with distance. This can be attributed either to a change in the governing physical processes in molecular clouds on spatial scales of about 1pc or to an AV dilution with distance in our map