The meaning and consequences of star formation criteria in galaxy models with resolved stellar feedback
The meaning and consequences of star formation criteria in galaxy models with resolved stellar feedback
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具有已解决的恒星反馈的星系模型中恒星形成标准的含义和后果
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发表时间：
2013
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影响因子：
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通讯作者：
N. Murray
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作者：
P. Hopkins;P. Hopkins;D. Narayanan;N. Murray
我们认为不同的标准，以确定恒星将在气体中形成星系尺度的影响，在模拟高（1 pc）分辨率，明确解决物理的巨分子云（GMC）的形成和破坏，恒星反馈超新星，辐射压力，恒星风和光加热。我们比较：（1）自重准则（基于局部维里参数和自引力气体在单个自由落体时间内坍缩到高密度的假设），（2）固定密度阈值，（3）分子气体定律，（4）温度阈值，（5）气体是Jeans不稳定的要求，（6）冷却时间短于动力学时间的准则;（7）收敛流准则。我们认为所有这些都在银河系（MW）和高密度（星暴或高红移）星系。有反馈存在，所有的模型产生相同的综合星星形成率（SFR），在良好的协议与Kennicutt关系;没有反馈都产生订单的数量级过多的SFR。这是完全依赖于反馈和独立的星星形成（SF）的法律，即使“本地”崩溃效率是100%。然而，预测的空间和密度分布强烈依赖于SF标准。由于星系盘内的冷却速率通常很快，而气体是湍流的，所以判据（4）-（7）非常“弱”，并且SF均匀地分布在盘的大部分区域（密度低至n = 0.01-0.1 cm^−3）。分子判据（3）局限于稍高的密度，但范围仍然很广;对于太阳附近的金属丰度，它几乎与固定的密度阈值n <$1 cm^-3相同（远低于中央MW或星暴系统的平均密度）。一个固定的密度阈值（2）总是可以选择最高的分辨密度，但必须根据模拟分辨率和单个星系的特性进行调整-在类似MW的模拟中工作良好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局部超密度，与星系模型或分辨率无关，并自动预测聚集SF。我们认为，这种SF模型（可能与其他次要标准）是最物理动机，并提出了显着的数值模拟具有较大的动态范围的优势。
We consider the effects of different criteria for determining where stars will form in gas on galactic scales, in simulations with high (1 pc) resolution, with explicitly resolved physics of Giant Molecular Cloud (GMC) formation and destruction, and stellar feedback from supernovae, radiation pressure, stellar winds and photoheating. 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 single free-fall time), (2) a fixed density threshold, (3) a molecular-gas law, (4) a temperature threshold, (5) a requirement that the gas be Jeans unstable, (6) a criteria that cooling times be shorter than dynamical times and (7) a convergent-flow criterion. We consider all of these in both a Milky Way (MW)-like and high-density (starburst or high-redshift) galaxy. With feedback present, all models produce identical integrated star formation rates (SFRs), in good agreement with the Kennicutt relation; without feedback all produce orders-of-magnitude excessive SFRs. This is totally dependent on feedback and independent of the star formation (SF) law, even if the ‘local’ collapse efficiency is 100 per cent. However, the predicted spatial and density distribution depend strongly on the SF criteria. Because cooling rates are generally fast within galaxy discs, and gas is turbulent, criteria (4)–(7) are very ‘weak’ and spread the SF uniformly over most of the disc (down to densities n ∼ 0.01–0.1 cm^−3). A molecular criterion (3) localizes to slightly higher densities, but still a wide range; for metallicity near solar, it is almost identical to a fixed density threshold at n ∼ 1 cm^−3 (well below the mean density in the central MW or starburst systems). A fixed density threshold (2) can always select the highest resolved densities, but must be adjusted both for simulation resolution and individual galaxy properties – the same threshold that works well in a MW-like simulation will select nearly all gas in a starburst. Binding criteria (1) tend to adaptively select the largest local overdensities, independent of galaxy model or resolution, and automatically predict clustered SF. We argue that this SF model (possible with other secondary criteria) is most physically motivated and presents significant numerical advantages in simulations with a large dynamic range.