M33中气体面密度的概率分布函数
The Probability Distribution Function of Gas Surface Density in M33
摘要：
M33的原子，分子和总气体表面密度的概率分布函数（PDF）的分辨率约为50 pc的区域，共享相干的形态属性，揭示了自引力指纹整个恒星形成盘。从中心区域到恒星形成盘边缘的大部分总气体PDF都很好地拟合了对数正态函数，其宽度径向向外减小。由于HI速度分散在整个盘上近似恒定，PDF宽度的减小与湍流ISM的较低马赫数一致，在大的银河中心半径处，HI的较高分数处于暖相。原子气体主要在面柱密度低于N $_{H}^{lim}$ =2.5 × 10 $^{21}$ ~cm $^{-2}$时被发现，N $_{H}^{lim}$具有小的径向变化。分子气体的PDF不显示强烈的偏离对数正态函数的分子分数高的中心区域。在这里，恒星形成的高压力和速率将PDF塑造为对数正态函数，在空间分辨的所有柱密度下分散具有强烈反馈的自引力复合物。在N $_H^{lim}$附近和上方，在定义明确的南旋臂和在较大的银河系中心半径处延伸的连续致密细丝中，发现了分子的幂律PDF;这在沿着恒星形成周期的不同演化阶段的云样本中很明显。在灯丝中，近一半的分子气体偏离对数正态概率密度函数，在恒星形成前的分子复合物中也观察到幂律。幂律的斜率在-1和-2之间。这个斜率，结合显示幂律PDF的不同部分来自哪里的地图，表明分子云复合物内的密度呈幂律分层，这与自引力的主导作用一致。
英文摘要：
The probability distribution functions (PDFs) for atomic, molecular, and total gas surface densities of M33 are determined at a resolution of about 50~pc over regions that share coherent morphological properties to unveil fingerprints of self-gravity across the star-forming disk. Most of the total gas PDFs from the central region to the edge of the star-forming disk are well-fitted by log-normal functions whose width decreases radially outwards. Because the HI velocity dispersion is approximately constant across the disk, the decrease of the PDF width is consistent with a lower Mach number for the turbulent ISM at large galactocentric radii where a higher fraction of HI is in the warm phase. The atomic gas is found mostly at face-on column densities below N$_{H}^{lim}$=2.5 10$^{21}$~cm$^{-2}$, with small radial variations of N$_{H}^{lim}$. The molecular gas PDFs do not show strong deviations from log-normal functions in the central region where molecular fractions are high. Here the high pressure and rate of star formation shapes the PDF as a log-normal function dispersing self-gravitating complexes with intense feedback at all column densities that are spatially resolved. Power law PDFs for the molecules are found near and above N$_H^{lim}$, in the well defined southern spiral arm and in a continuous dense filament extending at larger galactocentric radii; this is evident in cloud samples at different evolutionary stages along the star formation cycle. In the filament nearly half of the molecular gas departs from a log-normal PDF and power laws are also observed in pre-star forming molecular complexes. The slope of the power law is between -1 and -2. This slope, combined with maps showing where the different parts of the power law PDFs come from, suggest a power-law stratification of density within molecular cloud complexes, which is consistent with the dominance of self-gravity.
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