Schmidt和Kennicutt-Schmidt恒星形成定律之间的关系及其对数值模拟的影响
On the relation between the Schmidt and Kennicutt-Schmidt star formation laws and its implications for numerical simulations
摘要：
当在大尺度上平均时，观察到星系中的恒星形成遵循经验Kennicutt-Schmidt（KS）定律，表面密度高于恒定阈值。虽然观察到的定律涉及表面密度，但理论模型和模拟通常与体积密度定律（即施密特定律）一起工作。我们推导出的表面密度，体积密度和压力方面表示的恒星形成的法律之间的解析关系，我们展示了这些关系如何依赖于参数，如多相星际介质的有效状态方程。我们的分析关系使我们能够实现所观察到的表面密度的法律模拟。因为我们对恒星形成的处方参数是可观测的，我们不能自由地调整它们来匹配观测结果。我们测试我们的理论框架，采用高分辨率模拟孤立的盘星系，假设一个有效的状态方程的多相星际介质。我们能够重现恒星形成的阈值和斜率和归一化的任意输入KS法律没有调整任何参数和非常小的散射，即使是不稳定的星系，即使我们使用差的数值分辨率。此外，我们可以对任意有效状态方程这样做。因此，我们的处方使星系的模拟能够绕过我们目前无法模拟恒星形成的问题。另一方面，事实上，我们可以重现任意的输入阈值和KS法律，而不仅仅是特定的挑选出的性质，表明模拟缺乏物理和/或分辨率来模拟多相星际介质只能提供有限的洞察观察到的恒星形成规律的起源。
英文摘要：
When averaged over large scales, star formation in galaxies is observed to follow the empirical Kennicutt-Schmidt (KS) law for surface densities above a constant threshold. While the observed law involves surface densities, theoretical models and simulations generally work with volume density laws (i.e. Schmidt laws). We derive analytic relations between star formation laws expressed in terms of surface densities, volume densities, and pressures and we show how these relations depend on parameters such as the effective equation of state of the multiphase interstellar medium. Our analytic relations enable us to implement observed surface density laws into simulations. Because the parameters of our prescription for star formation are observables, we are not free to tune them to match the observations. We test our theoretical framework using high-resolution simulations of isolated disc galaxies that assume an effective equation of state for the multiphase interstellar medium. We are able to reproduce the star formation threshold and both the slope and the normalisation of arbitrary input KS laws without tuning any parameters and with very little scatter, even for unstable galaxies and even if we use poor numerical resolution. Moreover, we can do so for arbitrary effective equations of state. Our prescription therefore enables simulations of galaxies to bypass our current inability to simulate the formation of stars. On the other hand, the fact that we can reproduce arbitrary input thresholds and KS laws, rather than just the particular ones picked out by nature, indicates that simulations that lack the physics and/or resolution to simulate the multiphase interstellar medium can only provide limited insight into the origin of the observed star formation laws.
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