Log-normal Star Formation Histories in Simulated and Observed Galaxies
Log-normal Star Formation Histories in Simulated and Observed Galaxies
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DOI：
10.3847/1538-4357/aa68e5
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发表时间：
2017-01
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影响因子：
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通讯作者：
B. Diemer;M. Sparre;L. Abramson;P. Torrey
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作者：
B. Diemer;M. Sparre;L. Abramson;P. Torrey
格拉德斯等人。最近提出，单个星系的恒星形成历史（SFH）的特征是时间上的对数正态函数，这意味着缓慢下降而不是快速淬灭。我们通过宇宙学模拟 Illustris 的理论 SFH 和观测推断的 SFH 来测试他们的猜想。虽然对数正态形式必然忽略诸如星暴之类的短暂特征，但它非常适合大多数 SFH 的整体形状。特别是，85% 的累积 SFH 的拟合误差在所形成的总恒星质量的 5% 以内，99% 的拟合误差在 10% 以内。对数正态模型的性能比常用的延迟τ模型更好，并且仅被具有三个以上自由参数的函数所取代。不良拟合大多出现在成为卫星后迅速熄灭的星系中。我们探索了归一化、峰值时间和半峰全宽的对数正态参数空间，发现模拟和观察的样本占据相似的区域，尽管 Illustris 预测平均而言更宽、更晚形成的 SFH。对数正态拟合的集合正确地再现了复杂的度量，例如伊拉斯里斯星系在恒星形成主序列上的演化，但高估了它们的猝灭时间尺度。 Illustris 中的 SFH 是一个多样化的群体，不由星系的任何一种物理属性决定，而是遵循紧密的关系，其中 。我们表明，这种关系可以通过暗物质晕的增长与其星系之间的密切联系来定性（尽管不是定量）解释。
Gladders et al. have recently suggested that the star formation histories (SFHs) of individual galaxies are characterized by a log-normal function in time, implying a slow decline rather than rapid quenching. We test their conjecture on theoretical SFHs from the cosmological simulation Illustris and on observationally inferred SFHs. While the log-normal form necessarily ignores short-lived features such as starbursts, it fits the overall shape of the majority of SFHs very well. In particular, 85% of the cumulative SFHs are fitted to within a maximum error of 5% of the total stellar mass formed, and 99% to within 10%. The log-normal performs systematically better than the commonly used delayed-τ model, and is superseded only by functions with more than three free parameters. Poor fits are mostly found in galaxies that were rapidly quenched after becoming satellites. We explore the log-normal parameter space of normalization, peak time, and full width at half maximum, and find that the simulated and observed samples occupy similar regions, though Illustris predicts wider, later-forming SFHs on average. The ensemble of log-normal fits correctly reproduces complex metrics such as the evolution of Illustris galaxies across the star formation main sequence, but overpredicts their quenching timescales. SFHs in Illustris are a diverse population not determined by any one physical property of galaxies, but follow a tight relation, where . We show that such a relation can be explained qualitatively (though not quantitatively) by a close connection between the growth of dark matter halos and their galaxies.