2016A&A...588A..30S

We present new measurements of the dust emissivity index, β, for the high-mass, star-forming OMC 2/3 filament. We combined 160-500µm data from Herschel with long-wavelength observations at 2mm and fit the spectral energy distributions across a ≃2pc long, continuous section of OMC 2/3 at 15000AU (0.08pc) resolution. With these data, we measured β and reconstructed simultaneously the filtered-out large-scale emission at 2mm. We implemented both variable and fixed values of β, finding that β=1.7-1.8 provides the best fit across most of OMC 2/3. These β values are consistent with a similar analysis carried out with filtered Herschel data. Thus, we show that β values derived from spatial filtered emission maps agree well with those values from unfiltered data at the same resolution. Our results contradict the very low β values (∼0.9) previously measured in OMC 2/3 between 1.2mm and 3.3mm data, which we attribute to elevated fluxes in the 3.3mm observations. Therefore, we find no evidence of rapid, extensive dust grain growth in OMC 2/3. Future studies with Herschel data and complementary ground-based long-wavelength data can apply our technique to obtain reliable determinations of β in nearby cold molecular clouds.