标题： 具有双对称螺旋磁场的盘星系中碰撞诱导磁重联的致密气体形成 显示英文标题

标题： Dense Gas Formation via Collision-induced Magnetic Reconnection in a Disk Galaxy with a BiSymmetric Spiral Magnetic Field

摘要： 近期，提出了碰撞诱导磁重联（CMR）机制来解释猎户座A巨型分子云中的致密丝状体形成。一个自然的问题是，CMR是否在银河系的其他地方起作用。为了回答这个问题，本文研究了在具有修改后的双对称螺旋（BSS）磁场的平坦旋转盘中，CMR的触发及其致密气体的产生。通过Athena++代码模拟了盘中磁场反转处的云-云碰撞。在代表温性中性介质的条件下，云-云碰撞在不同盘半径处成功触发了CMR。然而，由于热压主导，致密气体的形成受到阻碍，除非存在适度更强的初始磁场$\gtrsim5\mu$高斯。强场模型具有更大的 Lundquist 数$S_L$和较低的等离子体$\beta$，激活了碰撞中平面的磁团块不稳定性，否则这种不稳定性会被盘旋转所抑制。我们推测，如果更多的云沿磁场反转发生碰撞，则CMR可能是常见的。然而，在数值模拟中见证CMR过程，我们需要显著地以空间动态范围$\gtrsim10^6$来解析碰撞中平面。如果银河系的旋臂确实与BSS中的磁场反转相吻合，那么CMR可能在这些旋臂中创造了或维持了致密气体。高分辨率、高灵敏度的Zeeman/Faraday-旋转观测对于寻找具有螺旋磁场的CMR候选者至关重要。 显示英文摘要

摘要： Recently, a collision-induced magnetic reconnection (CMR) mechanism was proposed to explain a dense filament formation in the Orion A giant molecular cloud. A natural question is that whether CMR works elsewhere in the Galaxy. As an initial attempt to answer the question, this paper investigates the triggering of CMR and the production of dense gas in a flat-rotating disk with a modified BiSymmetric Spiral (BSS) magnetic field. Cloud-cloud collisions at field reversals in the disk are modeled with the Athena++ code. Under the condition that is representative of the warm neutral medium, the cloud-cloud collision successfully triggers CMR at different disk radii. However, dense gas formation is hindered by the dominating thermal pressure, unless a moderately stronger initial field $\gtrsim5\mu$G is present. The strong-field model, having a larger Lundquist number $S_L$ and lower plasma $\beta$, activates the plasmoid instability in the collision midplane, which is otherwise suppressed by the disk rotation. We speculate that CMR can be common if more clouds collide along field reversals. However, to witness the CMR process in numerical simulations, we need to significantly resolve the collision midplane with a spatial dynamic range $\gtrsim10^6$. If Milky Way spiral arms indeed coincide with field reversals in BSS, it is possible that CMR creates or maintains dense gas in the arms. High-resolution, high-sensitivity Zeeman/Faraday-Rotation observations are crucial for finding CMR candidates that have helical fields.