A Model for the Origin of Bursty Star Formation in Galaxies
A Model for the Origin of Bursty Star Formation in Galaxies
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DOI：
10.1093/mnras/stx2595
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发表时间：
2017-01
影响因子：
4.8
通讯作者：
C. Faucher-Giguère
中科院分区：
文献类型：
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作者：
C. Faucher-Giguère
我们提出了一个简单的分析模型来解释星系中恒星形成是时间稳定的还是爆发的。最近的模型解释了观测到的星系中恒星形成率和气体表面密度之间的Kennicutt-Schmidt关系是恒星反馈和重力之间平衡的结果。我们认为，当这样的平衡不能稳定维持时，爆发恒星的形成就会发生，并确定了星系规模的恒星形成应该发生爆发的两个区域：i)所有质量的星系都处于高红移(z>；~1)，以及ii)任何红移的星系都处于低质量(取决于气体分数)。在高红移时，超新星反馈的特征星系动力学时标变得太短，无法有效地响应星系盘中的引力崩塌(最近发现的星系核效应)，而在矮小星系中，恒星形成发生在太少的明亮恒星形成区域，无法有效地平均出来。由于早期宇宙中气体分数的升高，高红移时的爆发性也会增强。因此，我们的模型可以解释最近的高分辨率星系形成模拟所预测的在这些区域中的爆发恒星形成率，以及在局部矮小和高红移星系中观测推断的爆发恒星形成历史。在我们的模型中，爆发恒星的形成与超新星特别强的时空聚集有关。这样的星团可以促进星系风的形成，因此我们的模型也可以解释高红移大质量星系相对于其Z0星系所推断的高得多的风质量负载因子。
We propose a simple analytic model to understand when star formation is time-steady versus bursty in galaxies. Recent models explain the observed Kennicutt-Schmidt relation between star formation rate and gas surface densities in galaxies as resulting from a balance between stellar feedback and gravity. We argue that bursty star formation occurs when such an equilibrium cannot be stably sustained, and identify two regimes in which galaxy-scale star formation should be bursty: i) at high redshift (z>~1) for galaxies of all masses, and ii) at low masses (depending on gas fraction) for galaxies at any redshift. At high redshift, characteristic galactic dynamical timescales become too short for supernova feedback to effectively respond to gravitational collapse in galactic discs (an effect recently identified for galactic nuclei), whereas in dwarf galaxies star formation occurs in too few bright star-forming regions to effectively average out. Burstiness is also enhanced at high redshift owing to elevated gas fractions in the early Universe. Our model can thus explain the bursty star formation rates predicted in these regimes by recent high-resolution galaxy formation simulations, as well as the bursty star formation histories observationally-inferred in both local dwarf and high-redshift galaxies. In our model, bursty star formation is associated with particularly strong spatio-temporal clustering of supernovae. Such clustering can promote the formation of galactic winds and our model may thus also explain the much higher wind mass loading factors inferred in high-redshift massive galaxies relative to their z~0 counterparts.