2007MNRAS.378.1447F

We present a 127x63-deg² extinction map of the Anticentre of the Galaxy, based on < J - H > and < H - K > 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 < J - H >/< H - K > 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 A_V 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 A_V_ dilution with distance in our map.