WHAT DETERMINES THE DENSITY STRUCTURE OF MOLECULAR CLOUDS? A CASE STUDY OF ORION B WITH HERSCHEL
WHAT DETERMINES THE DENSITY STRUCTURE OF MOLECULAR CLOUDS? A CASE STUDY OF ORION B WITH HERSCHEL
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DOI：
10.1088/2041-8205/766/2/l17
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发表时间：
2013-03
期刊：
影响因子：
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通讯作者：
N. Schneider;P. Andre';V. Könyves;S. Bontemps;F. Motte;C. Federrath;D. Ward-Thompson;D. Arzoumanian-D.
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文献类型：
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作者：
N. Schneider;P. Andre';V. Könyves;S. Bontemps;F. Motte;C. Federrath;D. Ward-Thompson;D. Arzoumanian-D.
描述所有恒星形成过程的一个关键参数是气体的密度结构。在这封信中，我们利用了猎户座 B、天鹰座和北极星的赫歇尔柱密度图的概率分布函数 (PDF)，这些图是通过赫歇尔古尔德带巡天 (HGBS) 获得的。我们的目标是了解哪些物理过程影响 PDF 形状以及哪些签名。 Orion B (Aquila) 的 PDF 在 AV ∼ 3 (6) 之前显示低柱密度的对数正态分布，以及高柱密度的幂律尾部，与等效球形密度分布的 ρ∝r−2 分布一致。由于附近的 OB 恒星聚集体，猎户座 B 的 PDF 因外部压缩而变宽。非恒星形成北极星云的静止子区域的 PDF 接近对数正态，表明超音速湍流控制着密度分布。但我们还观察到北极星中包含突出细丝的子区域在 AV > 1 处与对数正态形状存在偏差。我们得出的结论是：(1) PDF 偏离对数正态形式的点并不能追踪恒星形成的通用 AV 阈值，(2) 统计密度涨落、间歇性和磁场可能导致早期云形成阶段的对数正态 PDF 超出，(3) 核心形成和/或细丝的整体塌陷和非等温气体分布导致幂律尾部，(4) 外部压缩拓宽了柱密度 PDF，与数值模拟一致。
A key parameter to the description of all star formation processes is the density structure of the gas. In this Letter, we make use of probability distribution functions (PDFs) of Herschel column density maps of Orion B, Aquila, and Polaris, obtained with the Herschel Gould Belt survey (HGBS). We aim to understand which physical processes influence the PDF shape, and with which signatures. The PDFs of Orion B (Aquila) show a lognormal distribution for low column densities until AV ∼ 3 (6), and a power-law tail for high column densities, consistent with a ρ∝r−2 profile for the equivalent spherical density distribution. The PDF of Orion B is broadened by external compression due to the nearby OB stellar aggregates. The PDF of a quiescent subregion of the non-star-forming Polaris cloud is nearly lognormal, indicating that supersonic turbulence governs the density distribution. But we also observe a deviation from the lognormal shape at AV > 1 for a subregion in Polaris that includes a prominent filament. We conclude that (1) the point where the PDF deviates from the lognormal form does not trace a universal AV -threshold for star formation, (2) statistical density fluctuations, intermittency, and magnetic fields can cause excess from the lognormal PDF at an early cloud formation stage, (3) core formation and/or global collapse of filaments and a non-isothermal gas distribution lead to a power-law tail, and (4) external compression broadens the column density PDF, consistent with numerical simulations.