Paper detail

All-sky Observational Evidence for An Inverse Correlation between Dust Temperature and Emissivity Spectral Index

We show that a one-component variable-emissivity-spectral-index model (the free-α model) provides more physically motivated estimates of dust temperature at the Galactic polar caps than one- or two-component fixed-emissivity-spectral-index models (fixed-α models) for interstellar dust thermal emission at far-infrared and millimeter wavelengths. For the comparison we have fit all-sky one-component dust models with fixed or variable emissivity spectral index to a new and improved version of the 210-channel dust spectra from the COBE-FIRAS, the 100 - 240 μm maps from the COBE-DIRBE and the 94 GHz dust map from the WMAP. The best model, the free-α model, is well constrained by data at 60-3000 GHz over 86 per cent of the total sky area. It predicts dust temperature (Tdust) to be 13.7-22.7 (+/-1.3) K, the emissivity spectral index (α) to be 1.2 - 3.1 (+/-0.3) and the optical depth (τ) to range 0.6 - 46 x 10^(-5) at ν0 = 900 GHz (λ0 = 333 μm) with a 23 per cent uncertainty. Using these estimates, we present all-sky evidence for an inverse correlation between the emissivity spectral index and dust temperature, which fits the relation α = 1/(δ+ω Tdust) with δ = -0.510 +/- 0.011 and ω = 0.059 +/- 0.001. This best model will be useful to cosmic microwave background experiments for removing foreground dust contamination and it can serve as an all-sky extended-frequency reference for future higher resolution dust models.