恒星形成判据在具有可分辨恒星反馈的星系模型中的意义和结果
The Meaning and Consequences of Star Formation Criteria in Galaxy Models with Resolved Stellar Feedback
摘要：
我们考虑不同的恒星形成标准对星系尺度的影响，在高分辨率模拟明确解决GMC和恒星反馈。我们比较：（1）自重力准则（基于局部维里参数和自重力气体在自由落体时间内坍缩至高密度的假设），（2）固定密度阈值，（3）分子气体定律，（4）温度阈值，（5）琼斯不稳定性要求，（6）冷却时间短于动力学时间的准则，以及（7）收敛流准则。我们认为这两个MW类和高密度（星爆）星系。有了反馈，所有的模型产生相同的综合恒星形成率（SFR），与肯尼库特关系。在没有反馈的情况下，所有这些都产生数量级的过量SFR。这是完全依赖于反馈和独立的SF法律。然而，SF的空间和密度分布强烈依赖于SF标准。由于冷却速率通常很快，气体是湍流的，所以判据（4）-（7）是“弱的”，并且SF均匀地分布在圆盘上（高于密度n~0.01-0.1 cm^-3）。分子判据（3）局限于更高的密度，但范围仍然很广;对于Z Z_solar，它类似于n~1 cm^-3处的密度阈值（远低于MW中心或星爆的平均密度）。固定密度阈值（2）总是可以选择最高的密度，但必须根据模拟分辨率和星系属性进行调整;在类似MW的模拟中起作用的相同阈值将选择几乎所有的气体。约束准则（1）倾向于自适应地选择最大的过密度，独立于星系模型或分辨率，并自动预测成簇的SF。我们认为，这种SF模型是最物理动机，并提出了显着的数值优势，在大动态范围的模拟。
英文摘要：
We consider the effects of different star formation criteria on galactic scales, in high-resolution simulations with explicitly resolved GMCs and stellar feedback. We compare: (1) a self-gravity criterion (based on the local virial parameter and the assumption that self-gravitating gas collapses to high density in a free-fall time), (2) a fixed density threshold, (3) a molecular-gas law, (4) a temperature threshold, (5) a Jeans-instability requirement, (6) a criteria that cooling times be shorter than dynamical times, and (7) a convergent-flow criterion. We consider these both MW-like and high-density (starburst) galaxies. With feedback present, all models produce identical integrated star formation rates (SFRs), in agreement with the Kennicutt relation. Without feedback all produce orders-of-magnitude excessive SFRs. This is totally dependent on feedback and independent of the SF law. However, the spatial and density distribution of SF depend strongly on the SF criteria. Because cooling rates are generally fast and gas is turbulent, criteria (4)-(7) are 'weak' and spread SF uniformly over the disk (above densities n~0.01-0.1 cm^-3). A molecular criterion (3) localizes to higher densities, but still a wide range; for Z Z_solar, it is similar to a density threshold at n~1 cm^-3 (well below mean densities in the MW center or starbursts). Fixed density thresholds (2) can always select the highest densities, but must be adjusted for simulation resolution and galaxy properties; the same threshold that works in a MW-like simulation will select nearly all gas in a starburst. Binding criteria (1) tend to adaptively select the largest over-densities, independent of galaxy model or resolution, and automatically predict clustered SF. We argue that this SF model is most physically-motivated and presents significant numerical advantages in large-dynamic range simulations.
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