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

Abstract

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 × 10²⁰ cm^-2 < N < 2 × 10²³ cm^-2. We determined the ratio of the 2.2 μm extinction coefficient to the 850μm 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 Σ_∗ follows a simple law Σ_∗ ∝ Σ_gas^β, with β ~ 2.