Investigating the Evolution of Dust Grains Within the Orion Molecular Cloud

Abstract

It is assumed that dust opacities in molecular clouds follow a constant power-law profile with an index, β. Recent studies of the Orion Molecular Cloud (OMC) 2/3 complex, however, show a flattening in the spectral energy distribution (SED) at λ > 2 mm on core scales, implying a non-constant β. The origin of this flattening is not yet known but amounts to elevated emission at 3.3 mm as measured by the Green Bank Telescope by roughly a factor of 2 compared to extrapolations of shorter wavelength (< 2 mm) data. This change in β may be due to the intrinsic properties of the dust grains themselves or it could be due to contamination from other sources of emission. We investigate the SED slopes in OMC 2/3 further using observations of six protostellar cores with NOEMA from 2.9 to 3.6 mm and ALMA-ACA in Bands 4 and 5. We confirm a flattened dust opacity index at ∼ 3 mm. Such flat SEDs at 3 mm wavelengths could have profound implications for our understanding of dust grain evolution and for how we derive masses from thermal dust emission. We discuss these implications and propose why such elevated emission may be detected on core scales in Orion.