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arXiv 1803.00007astro-ph.GA
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星系如何形成恒星：星系模拟中局部和全局恒星形成之间的联系

How galaxies form stars: the connection between local and global star formation in galaxy simulations

Vadim A. Semenov, Andrey V. Kravtsov, Nickolay Y. Gnedin

备注：
17 pages + appendix, 13 figures, 1 table; accepted for publication in ApJ
发表信息：
ApJ 861, 4 (2018)
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摘要：

使用一套孤立的$L_\star$星系模拟，我们表明，全球耗尽时间和恒星形成气体的质量分数在模拟星系表现出系统的和明确的趋势，作为当地的每自由落体时间的恒星形成效率的函数，$ε_{\rm ff}$，恒星反馈的强度，和恒星形成阈值。我们证明，这些趋势可以通过星系中全球恒星形成的简单物理模型来重现和解释。我们的模型是基于质量守恒和气体之间的恒星形成和非恒星形成状态的动力学和反馈过程的影响下，在一定的特征时间尺度循环的想法。无论是模拟结果和我们的模型预测表现出两个限制制度，而不同的依赖关系的全球星系的性质的局部参数。当$ε_{\rm ff}$很小时，反馈效率很低，总的恒星形成质量分数$f_{\rm sf}$与$ε_{\rm ff}$无关，而总的耗尽时间$τ_{\rm dep}$与$ε_{\rm ff}$成反比。当$ε_{\rm ff}$较大或反馈非常有效时，这些趋势相反：$f_{\rm sf} \propto ε_{\rm ff}^{-1}$和$τ_{\rm dep}$独立于$ε_{\rm ff}$，但与反馈强度成线性比例。我们还比较了我们的结果与所观察到的耗尽时间和质量分数的恒星形成和分子气体，并表明它们提供了互补的约束$ε_{\rm ff}$和反馈强度。我们表明，有用的限制$ε_{\rm ff}$也可以得到使用测量的耗尽时间和它的分散在不同的空间尺度上。

英文摘要：

Using a suite of isolated $L_\star$ galaxy simulations, we show that global depletion times and star-forming gas mass fractions in simulated galaxies exhibit systematic and well-defined trends as a function of the local star formation efficiency per freefall time, $ε_{\rm ff}$, strength of stellar feedback, and star formation threshold. We demonstrate that these trends can be reproduced and explained by a simple physical model of global star formation in galaxies. Our model is based on mass conservation and the idea of gas cycling between star-forming and non-star-forming states on certain characteristic time scales under the influence of dynamical and feedback processes. Both the simulation results and our model predictions exhibit two limiting regimes with rather different dependencies of global galactic properties on the local parameters. When $ε_{\rm ff}$ is small and feedback is inefficient, the total star-forming mass fraction, $f_{\rm sf}$, is independent of $ε_{\rm ff}$ and the global depletion time, $τ_{\rm dep}$, scales inversely with $ε_{\rm ff}$. When $ε_{\rm ff}$ is large or feedback is very efficient, these trends are reversed: $f_{\rm sf} \propto ε_{\rm ff}^{-1}$ and $τ_{\rm dep}$ is independent of $ε_{\rm ff}$ but scales linearly with the feedback strength. We also compare our results with the observed depletion times and mass fractions of star-forming and molecular gas and show that they provide complementary constraints on $ε_{\rm ff}$ and the feedback strength. We show that useful constraints on $ε_{\rm ff}$ can also be obtained using measurements of the depletion time and its scatter on different spatial scales.

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