Intermittency of interstellar turbulence: extreme velocity-shears and CO emission on milliparsec scale
Intermittency of interstellar turbulence: extreme velocity-shears and CO emission on milliparsec scale
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星际湍流的间歇性：毫秒尺度上的极端速度剪切和二氧化碳排放
DOI：
10.1051/0004-6361/200810963
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发表时间：
2009
影响因子：
6.5
通讯作者：
P. Hily
中科院分区：
文献类型：
--
作者：
E. Falgarone;J. Pety;P. Hily
目标。扩散气体凝聚成分子云和致密核心的速度很大程度上是由湍流耗散驱动的。这一进程仍然需要在行动中抓住并确定其特点。方法：研究方法。为了寻找北极星耀斑中低质量致密核的湍流和半透明环境的12CO(1−0)谱线发射的小尺度结构，我们用IRAM-PDB干涉仪观测了13个场的镶嵌。在弥散分子气体的小尺度结构研究中，马赛克的大小(1�×2�)与分辨率(4��)相比是前所未有的。结果。干涉仪数据揭示了八个脆弱而细长的结构，厚度小至≈3Mpc(600AU)，长度高达70Mpc，接近马赛克的大小。这些不是细丝，因为一旦与短间距数据合并，PdBI结构在空间和速度-空间上似乎是更大规模结构的尖锐边缘。八分之六的行星以不同的速度和不同的位置角形成准平行的对子。这不可能是机会对齐的结果。这三对恒星的速度切变估计值包括在不形成恒星的区域(S−1 PC−1高达780公里)测量到的最高值。PdBI结构的CO柱密度在N(CO)=10 14~10 15 cm−2的范围内，用几种方法估计它们的H2密度不超过几个10 3 cm−3。由于较大尺度的结构具有锋利的边缘(成对的结构几乎没有重叠)，它们必须是CO排放的薄层。对于尖边延伸(双)结构，我们称它们为See(D)S。这些边缘在毫秒尺度上标志着富CO组分和12 CO(1−0)线中未被检测到的气体之间的过渡，因为它的CO丰度较低，推测是冷的中性介质。结论。我们认为，这些SEE(D)S是首次直接探测到的星际湍流间歇性的表现。大的速度切变揭示了一个强烈的应变场，导致了一个比平均高出几个数量级的局部耗散率，可能是在薄CO层的起始处。
Aims. The condensation of diffuse gas into molecular clouds and dense cores occurs at a rate driven largely by turbulent dissipation. This process still has to be caught in action and characterized. Methods. We observed a mosaic of 13 fields with the IRAM-PdB interferometer (PdBI) to search for small-scale structure in the 12 CO(1−0) line emission of the turbulent and translucent environment of a low-mass dense core in the Polaris Flare. The large size of the mosaic (1 � × 2 � ) compared to the resolution (4 �� ) is unprecedented in the study of the small-scale structure of diffuse molecular gas. Results. The interferometer data uncover eight weak and elongated structures with thicknesses as small as ≈3 mpc (600 AU) and lengths up to 70 mpc, close to the size of the mosaic. These are not filaments because once merged with short-spacings data, the PdBI-structures appear to be the sharp edges, in space and velocity-space, of larger-scale structures. Six out of eight form quasiparallel pairs at different velocities and different position angles. This cannot be the result of chance alignment. The velocity-shears estimated for the three pairs include the highest values ever measured in regions that do not form stars (up to 780 km s −1 pc −1 ). The CO column density of the PdBI-structures is in the range N(CO) = 10 14 to 10 15 cm −2 and their H2 density, estimated in several ways, does not exceed a few 10 3 cm −3 . Because the larger scale structures have sharp edges (with little or no overlap for those that are pairs), they have to be thin layers of CO emission. We call them SEE(D)S for sharp-edged extended (double) structures. These edges mark a transition, on the milliparsec scale, between a CO-rich component and a gas undetected in the 12 CO(1−0) line because of its low CO abundance, presumably the cold neutral medium. Conclusions. We propose that these SEE(D)S are the first directly-detected manifestations of the intermittency of interstellar turbulence. The large velocity-shears reveal an intense straining field, responsible for a local dissipation rate several orders of magnitude above average, possibly at the origin of the thin CO layers.
影响因子：
3.2
作者：
V. Mannings;A. Boss;S. Russell
通讯作者：
V. Mannings;A. Boss;S. Russell