AI 中文总结
本研究通过POLARIS工具开展多尺度合成尘埃偏振观测，探究从分子云到无恒星核的退偏振机制，明确了不同柱密度下主导退偏振的因素，为约束尘埃物理特性提供了方法。
AI 中文摘要
从分子云到无恒星核的亚毫米偏振尘埃辐射观测常报道偏振度（p）随尘埃辐射强度（I）增加而降低的特征，该特征通常被归因于尘埃颗粒的排列损失或磁场的几何效应，但具体贡献仍不明确。为探究退偏振的机制，我们使用POLARIS工具，通过辐射扭矩（RATs）机制，对磁取向尘埃颗粒开展850μm处的多尺度合成尘埃偏振观测。我们采用三个具有不同磁能水平的坍缩云模型，探究尘埃磁特性及颗粒生长对尘埃偏振的影响。在氢柱密度NH<10²¹-10²²cm⁻²时，磁场几何效应是主导退偏振机制；当颗粒生长超过0.5μm且为含大铁簇的超顺磁（SPM）颗粒时，RATs在高柱密度下仍有效，颗粒排列损失仅在NH>10²³cm⁻²时对退偏振有贡献；若不满足上述任一条件，对于颗粒生长不足的情况，排列损失，或对于顺磁颗粒或含小铁簇的SPM颗粒，气体阻尼降低颗粒排列效率的情况，都会在NH>10²²cm⁻²时成为主导退偏振机制，与模拟中磁场线的缠结程度无关。最终，我们表明可通过p-I斜率和核中心的平均p来识别无恒星核内部的退偏振机制及潜在尘埃物理特性。
英文摘要
Submillimeter observations of polarized dust emission from molecular clouds to starless cores frequently report a decrease in polarization fraction (p) with increasing dust emission intensity (I). This feature is commonly attributed to the alignment loss of dust grains or the geometrical effects of magnetic fields, yet, the detailed contributions remain unclear. To investigate the mechanism responsible for the depolarization, we use POLARIS to perform the multiscale synthetic dust polarization observations at $850μm$ from magnetically aligned dust grains by RAdiative Torques (RATs) mechanism. We adopt three collapsing cloud models with different magnetic energy levels and explore the effects of grain magnetic properties and grain growth on dust polarization. The field geometrical effect is the dominant depolarization mechanism at $N_{\rm H}<10^{21}-10^{22}\rm cm^{-2}$. We find that if grains grow beyond $>0.5μm$ and are superparamagnetic (SPM) with large iron clusters, RATs remain effective at high column densities, and grain alignment loss contributes to depolarization only at $N_{\rm H} > 10^{23}\rm cm^{-2}$. If neither of these conditions is satisfied, the alignment loss (in cases of insufficient grain growth); or the reduced grain alignment efficiency by gaseous damping (for paramagnetic grains or SPM grains with small iron cluster sizes) can become the dominant depolarization mechanism at $N_{\rm H} > 10^{22}\rm cm^{-2}$, regardless of how tangled the magnetic field lines in our simulation. Finally, we show that the depolarization mechanism and the underlying dust physical properties inside starless cores may be identified through the $p-I$ slope and the mean p at the core center.
CommentsAccepted to be published in ApJ. 24 pages, 11 figures in Main text, 8 pages in Appendix
