Observational Constraints on Submillimeter Dust Opacity

Abstract

Infrared extinction maps and submillimeter dust continuum maps are powerful probes of the density structure in the envelope of star-forming cores. We make a direct comparison between infrared and submillimeter dust continuum observations of the low-mass Class 0 core, B335, to constrain the ratio of submillimeter to infrared opacity (κ_smm/κ_ir) and the submillimeter opacity power-law index (κ vprop λ^-β). Using the average value of theoretical dust opacity models at 2.2 μm, we constrain the dust opacity at 850 and 450 μm. Using new dust continuum models based upon the broken power-law density structure derived from interferometric observations of B335 and the infall model derived from molecular line observations of B335, we find that the opacity ratios are \frac{\kappa _{850}}{\kappa _{2.2}} = (3.21{--}4.80)^{+0.44}_{-0.30} \times 10^{-4} and \frac{\kappa _{450}}{\kappa _{2.2}} = (12.8{--}24.8)^{+2.4}_{-1.3} \times 10^{-4}with a submillimeter opacity power-law index of β_smm = (2.18-2.58)^+0.30 _-0.30. The range of quoted values is determined from the uncertainty in the physical model for B335. For an average 2.2 μm opacity of 3800 ± 700 cm² g^-1, we find a dust opacity at 850 and 450 μm of κ₈₅₀ = (1.18-1.77)^+0.36 _-0.24 and κ₄₅₀ = (4.72-9.13)^+1.9 _-0.98 cm² g^-1 of dust. These opacities are from (0.65-0.97)κ^OH5 ₈₅₀ of the widely used theoretical opacities of Ossenkopf and Henning for coagulated ice grains with thin mantles at 850 μm.