Dust emission and extinction in the Orion OMC-3 cloud

Dust is an important tracer of the structure of interstellar clouds, as well as a central factor in the thermal balance and chemistry of the clouds. Our knowledge of the dust properties is nevertheless incomplete, especially regarding the dense star-forming clouds. The aim is to study dust evolution in the Orion Molecular Cloud 3 (OMC-3) and how uncertainty regarding dust properties affects estimates of the radiation field and the cloud mass. We constructed three-dimensional radiative transfer (RT) models to fit the far-infrared (FIR) observations of dust emission in the OMC-3 field and used near-infrared (NIR) extinction measurements as additional constraints. We examined fits to the dense star-forming filaments and to the surrounding cloud, including some tests with spatial dust property variations. The 160-250,μm observations of dust emission could be fitted moderately well with any of the dust models tested, but few models are consistent with the measured NIR extinction. The best match to observations is found with dust models such as the THEMIS model of large porous grains, with or without ice mantles, and with mean grain sizes up to ∼ 0.3,μm. The flattening of the NIR extinction curve excludes larger grain sizes, except possibly in the central ridge. Compared to models of lower column density clouds, the results were relatively insensitive to the line-of-sight (LOS) cloud size and the spectral shape of the heating radiation field. In addition, the effect of embedded stars remained very localised in OMC-3. The results suggest that the dust in the OMC-3 region is evolved with a grain of average size a=0.1-0.3,μm, potentially with ice mantles.