Dust Emissivity in the Star-Forming Filament OMC 2/3

TL;DR

This study measures the dust emissivity index beta in the OMC 2/3 star-forming filament using combined Herschel and long-wavelength data, finding consistent beta values around 1.7-1.8 and no evidence of rapid dust grain growth.

Contribution

The paper introduces a method to accurately determine dust emissivity index beta by combining filtered and unfiltered data, resolving previous discrepancies in measurements.

Findings

Beta values are around 1.7-1.8 across OMC 2/3.

No evidence of rapid dust grain growth in the region.

Filtered and unfiltered data yield consistent beta measurements.

Abstract

We present new measurements of the dust emissivity index, beta, for the high-mass, star-forming OMC 2/3 filament. We combine 160-500 um data from Herschel with long-wavelength observations at 2 mm and fit the spectral energy distributions across a ~ 2 pc long, continuous section of OMC 2/3 at 15000 AU (0.08 pc) resolution. With these data, we measure beta and reconstruct simultaneously the filtered-out large-scale emission at 2 mm. We implement both variable and fixed values of beta, finding that beta = 1.7 - 1.8 provides the best fit across most of OMC 2/3. These beta values are consistent with a similar analysis carried out with filtered Herschel data. Thus, we show that beta 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 beta values (~ 0.9) previously measured in OMC 2/3 between 1.2 mm and 3.3 mm data, which we attribute to elevated fluxes in the 3.3 mm observations. Therefore, we find no evidence or 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 robust determinations of beta in nearby cold molecular clouds.