Formation of dense structures induced by filament collisions. Correlation of density, kinematics, and magnetic field in the Pipe nebula
Formation of dense structures induced by filament collisions. Correlation of density, kinematics, and magnetic field in the Pipe nebula
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由细丝碰撞引起致密结构的形成。
DOI：
10.1051/0004-6361/201425234
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发表时间：
2015
影响因子：
6.5
通讯作者：
C. G.
中科院分区：
文献类型：
--
作者：
Frau;P.;Girart;J. M.;Alves;F. O.;Franco;G. A. P.;Onishi;T.;and Roman-Zuniga;C. G.
管状星云是一种缺乏恒星形成反馈的分子云，具有相对简单的形态和速度结构。这使得它成为通过碰撞测试云演化的理想目标。我们的目标是对这种相对简单的云绘制一个全面的图像，以便更好地了解大尺度分子云的形成和演化。方法利用档案资料比较整个云团的光学偏振特性、视觉消光、13co速度和线宽，以确定观测资料之间的变化趋势。结果管状星云大致可分为两个方向和速度范围不同的细丝：E-W为2 ~ 4 km s-1， N-S为6 ~ 7 km s-1。两个细丝在碗状区域重叠，在那里气体显示出从2到7 km s-1的速度梯度。与管状星云的其他部分相比，碗状气体看起来密度更大，线宽也更大。此外，碗形处的偏振数据显示出较低的角色散和较高的偏振度。碗状岩心倾向于在空间中聚集，并遵循13co的速度梯度。在茎中，核倾向于聚集在具有与碗相似属性的区域。结论：速度模式表明碗状区域的纤维之间发生了碰撞。磁场似乎在震波区被压缩和加强。密度和磁场强度按与alfv<s:1>马赫数相似的比例增加表明，在熔剂冻结条件下，在低alfv<s:1>马赫数下存在连续激波。激波区似乎加强了致密核的形成和聚集。
ContextThe Pipe nebula is a molecular cloud that lacks star formation feedback and has a relatively simple morphology and velocity structure. This makes it an ideal target for testing cloud evolution through collisions.AimsWe aim at drawing a comprehensive picture of this relatively simple cloud to better understand the formation and evolution of molecular clouds on large scales.MethodsWe use archival data to compare the optical polarization properties, the visual extinction, and the13CO velocities and linewidths of the entire cloud in order to identify trends among the observables.ResultsThe Pipe nebula can be roughly divided into two filaments with different orientations and gas velocity ranges: E–W at 2−4 km s-1and N–S at 6–7 km s-1. The two filaments overlap at the bowl, where the gas shows a velocity gradient spanning from 2 to 7 km s-1. Compared to the rest of the Pipe nebula, the bowl gas appears to be denser and exhibits larger linewidths. In addition, the polarization data at the bowl shows lower angular dispersion and higher polarization degree. Cores in the bowl tend to cluster in space and to follow the13CO velocity gradient. In the stem, cores tend to cluster in regions with properties similar to those of the bowl.ConclusionsThe velocity pattern points to a collision between the filaments in the bowl region. The magnetic field seems to be compressed and strengthened in the shocked region. The proportional increase in density and magnetic field strength by a factor similar to the Alfvénic Mach number suggests a continuous shock at low Alfvénic Mach number under the flux-freezing condition. Shocked regions seem to enhance the formation and clustering of dense cores.