标题： 向辐射力矩和磁弛豫引起的晶粒对齐和破坏的一般理论迈进 显示英文标题

标题： Toward A General Theory of Grain Alignment and Disruption by Radiative Torques and Magnetic Relaxation

摘要： 我们推广了磁增强辐射扭矩（MRAT）对齐理论，适用于由无量纲参数$U/(n_{1}T_{2})$描述的一般天体物理环境，其中$U$表示局部辐射强度，$n_{1}=n_{\rm H}/(10{\rm cm}^{-3})$表示氢密度，$T_{2}=T_{\rm gas}/100{\rm K}$表示气体温度。 我们首先推导出产生高-J吸引子所需的临界磁弛豫$\delta_{\rm mag,cri}$，针对不同的RAT模型和局部条件进行研究，并发现当辐射场更强时，$\delta_{\rm mag,cri}$必须更大。 随后，我们数值研究了MRAT机制在考虑气体碰撞和磁涨落的情况下对颗粒对齐和旋转破坏的影响。 我们发现，在碰撞主导（CD）区域（$U/(n_{1}T_{2})\leq 1$），碰撞和磁激发可以缓慢地将大颗粒从低-J旋转传输到高-J吸引子，由于MRATs的作用，在$\sim 10-100$阻尼时间内导致完美的{\it 慢速对齐}。 然而，在辐射主导（RD）区域（$U/(n_{1}T_{2})>1$），只有部分颗粒可以通过MRATs快速对齐到高-J吸引子，而大部分颗粒由于强辐射力矩被限制在低-J旋转，这是一种我们称之为{\it 辐射力矩（RAT）捕获}的新效应。 对于极端辐射场的$U/(n_{1}T_{2})>10^{4}$，磁弛豫在颗粒对齐中的效率被抑制，颗粒仅由RATs决定的快速对齐和破坏。 我们量化了在高-J吸引子处具有快速对齐的晶粒比例，$f_{\rm high-J}^{\rm fast}$，对于不同的RAT模型、磁弛豫和$U/(n_{1}T_{2})$，发现最大$f_{\rm high-J}^{\rm fast}$可通过MRATs达到$45\%$，并通过RATs达到$22\%$。 显示英文摘要

摘要： We generalize the magnetically enhanced radiative torque (MRAT) alignment theory for general astrophysical environments described by a dimensionless parameter $U/(n_{1}T_{2})$ with $U$ local radiation strength, $n_{1}=n_{\rm H}/(10{\rm cm}^{-3})$ the hydrogen density, and $T_{2}=T_{\rm gas}/100{\rm K}$ the gas temperature. We first derive the critical magnetic relaxation $\delta_{\rm mag,cri}$ required to produce high-J attractors for different RAT models and local conditions and find that $\delta_{\rm mag,cri}$ must be larger for stronger radiation fields. We then numerically study the grain alignment and rotational disruption by the MRAT mechanism taking into account gas collisions and magnetic fluctuations. We find that, for the collision-dominated (CD) regime ($U/(n_{1}T_{2})\leq 1$), collisional and magnetic excitations can slowly transport large grains from low-J rotation to high-J attractors, leading to the perfect {\it slow alignment} within $\sim 10-100$ damping times due to MRATs. However, for the radiation-dominated (RD) regime ($U/(n_{1}T_{2})>1$), only a fraction of grains can be fast aligned at high-J attractors by MRATs, and the majority of grains are trapped at low-J rotation due to strong radiative torques, a new effect we term {\it radiative torque (RAT) trapping}. For extreme radiation fields of $U/(n_{1}T_{2})>10^{4}$, the efficiency of magnetic relaxation on grain alignment is suppressed, and grains only have fast alignment and disruption purely determined by RATs. We quantified the fraction of grains with fast alignment at high-J attractors, $f_{\rm high-J}^{\rm fast}$, for different RAT models, magnetic relaxation, and $U/(n_{1}T_{2})$, and found that the maximum $f_{\rm high-J}^{\rm fast}$ can reach $45\%$ by MRATs and $22\%$ by RATs.