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A pressure dependence for bound and unbound clusters

机译：约束和非约束簇的压力依赖性

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Hierarchical structure in gas and young stars produces clusters in high-density regions where the individual stellar orbits rapidly mix. For a fixed density at the onset of gas collapse (e.g. determined by changes in the ionization equilibrium and grain properties), the efficiency of star formation is automatically high in the high-density regions of giant molecular clouds. Thus, bound cluster formation follows somewhat trivially from hierarchical structure. The density where the efficiency is high enough to produce a bound cluster depends on the dispersion of the density probability distribution function (pdf), decreasing for higher dispersions and making bound cluster formation more likely. Similarly, the mass fraction of star formation in the form of bound clusters increases with the pdf dispersion. Because this dispersion is related to the turbulent Mach number, and also to the interstellar medium pressure and star-formation rate per unit volume, it follows that high-pressure or highly active regions tend to produce bound clusters, while low-pressure and inactive regions tend to produce stars in unbound associations.
机译：气体恒星和年轻恒星的层级结构在高密度区域产生星团，各个恒星轨道迅速混合。对于气体崩塌开始时的固定密度（例如，由电离平衡和晶粒特性的变化确定），在巨大分子云的高密度区域中自动形成恒星的效率很高。因此，束缚簇的形成在某种程度上是从分层结构中得出的。效率足以产生束缚簇的密度取决于密度概率分布函数（pdf）的离散度，对于更高的离散度则降低，并使束缚簇的形成更有可能。同样，束缚星团形式的恒星形成的质量分数随pdf色散而增加。由于这种分散与湍流马赫数有关，还与星际介质压力和单位体积的恒星形成率有关，因此，高压或高活性区域倾向于产生束缚簇，而低压和非活性区域倾向于倾向于以无界的联想产生恒星。

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