基于极化的風粒对齐与尘埃演化物理 (GRADE-POL)。I.针对孤立无星核心的尘埃极化建模

由对准的星际尘埃引起的极化是探讨宇宙磁场、尘埃性质的重要工具，并在表征宇宙微波背景极化以及其他来源方面具有挑战性。为了将尘埃极化确立为可靠的工具，需彻底研究grain alignment process的 physics。Magnetically enhanced Radiative Torque (MRAT) alignment 是唯一能够诱导 grains 与磁场高度有效对齐的机制，这是极化观测中对diffuse interstellar medium所必需的。我们的 numerical modelling of dust polarisation using the MRAT theory demonstrated that the alignment efficiency of starlight polarisation ($p_{\rm ext}/A_{\rm V}$) and the degree of thermal dust polarisation ($p_{\rm em}$) first decrease slowly with increasing visual extinction ($A_{\rm V}$) and then falls steeply as $\propto A^{-1}_{\rm V}$ at large $A_{\rm V}$ due to the loss of grain alignment, which explains the phenomenon known as polarisation holes。Visual extinction at the transition from shallow to steep slope ($A^{\rm loss}_{\rm V}$) increases with the maximum grain size。By applying physical profiles suitable for a starless core 109 in the Pipe Nebula (Pipe-109), our model successfully reproduces the existing observations of starlight polarisation at R-band ($0.65\,\mu$m) and H-band ($1.65\,\mu$m), as well as emission polarisation at submillimetre ($870\,\mu$m)。Successful modelling of observational data requires perfect alignment of large grains as evidence of the MRAT mechanism, and larger maximum size with higher elongation at higher $A_{\rm V}$。The latter reveals the first evidence for the new model of anisotropic grain growth induced by magnetic grain alignment。