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