Herschel-Planck dust optical-depth and column-density maps I. Method description and results for Orion

We present high-resolution, high dynamic range column-density and color-temperature maps of the Orion complex using a combination of Planck dust-emission maps, Herschel dust-emission maps, and 2MASS NIR dust-extinction maps. The column-density maps combine the robustness of the 2MASS NIR extinction maps with the resolution and coverage of the Herschel and Planck dust-emission maps and constitute the highest dynamic range column-density maps ever constructed for the entire Orion complex, covering 0.01 mag < A(K) < 30 mag, or 2 x 10(20) cm(-2) < N < 5 x 10(23) cm(-2). We determined the ratio of the 2.2 mu m extinction coefficient to the 850 mu m opacity and found that the values obtained for both Orion A and B are significantly lower than the predictions of standard dust models, but agree with newer models that incorporate icy silicate-graphite conglomerates for the grain population. We show that the cloud projected probability distribution function, over a large range of column densities, can be well fitted by a simple power law. Moreover, we considered the local Schmidt-law for star formation, and confirm earlier results, showing that the protostar surface density Sigma(*) follows a simple law Sigma(*) proportional to Sigma(beta)(gas), with beta similar to 2.