How to Measure Galaxy Star Formation Histories. II. Nonparametric Models
How to Measure Galaxy Star Formation Histories. II. Nonparametric Models
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DOI：
10.3847/1538-4357/ab133c
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发表时间：
2018-11
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通讯作者：
J. Leja;A. Carnall;Benjamin D. Johnson;C. Conroy;J. Speagle
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作者：
J. Leja;A. Carnall;Benjamin D. Johnson;C. Conroy;J. Speagle
非参数星星形成历史（SFH）一直被认为是星系光谱能量分布（SED）建模的“黄金标准”，因为它们足够灵活，可以描述SFH形状的全部多样性，而参数模型排除了这些形状的先验的一个重要部分。然而，即使是高质量的观测，这种灵活性也没有完全受到限制，因此选择一个动机良好的先验至关重要。在这里，我们使用SED拟合代码Prospector通过拟合SFH来模拟从一组不同的输入SFH生成的紫外-红外光度测定来探索不同非参数先验的影响。首先，我们确认，非参数SFHs恢复输入SFHs与更少的偏见和返回更准确的错误比参数SFHs。我们进一步发现，虽然非参数SFH鲁棒地恢复输入SFH的整体形状，作为时间的函数的后星星形成率（SFR（t））的大小和形状的主要决定因素是先验的选择，而不是光度噪声。作为一个实际的演示，我们适合从银河系和质量大会调查和测量散射的前0.1德克斯的质量，0.8德克斯在SFR 1亿年，和0.2德克斯的质量加权年龄，与最蓝的恒星形成的星系表现出最灵敏的紫外-红外光度计。非参数模型的一个重要区别特征是SFR（t）变化的特征时间尺度。这种差异控制星系是否组装在爆发或稳态星星形成，分别对应于（反馈为主/吸积为主）模型的星系形成和（较大/较小）的置信区间来自SED拟合。高质量的光谱学有可能进一步区分这些提出的SFR（t）模型。
Nonparametric star formation histories (SFHs) have long promised to be the “gold standard” for galaxy spectral energy distribution (SED) modeling as they are flexible enough to describe the full diversity of SFH shapes, whereas parametric models rule out a significant fraction of these shapes a priori. However, this flexibility is not fully constrained even with high-quality observations, making it critical to choose a well-motivated prior. Here, we use the SED-fitting code Prospector to explore the effect of different nonparametric priors by fitting SFHs to mock UV–IR photometry generated from a diverse set of input SFHs. First, we confirm that nonparametric SFHs recover input SFHs with less bias and return more accurate errors than do parametric SFHs. We further find that, while nonparametric SFHs robustly recover the overall shape of the input SFH, the primary determinant of the size and shape of the posterior star formation rate as a function of time (SFR(t)) is the choice of prior, rather than the photometric noise. As a practical demonstration, we fit the UV–IR photometry of ∼6000 galaxies from the Galaxy and Mass Assembly survey and measure scatters between priors to be 0.1 dex in mass, 0.8 dex in SFR100 Myr, and 0.2 dex in mass-weighted ages, with the bluest star-forming galaxies showing the most sensitivity. An important distinguishing characteristic for nonparametric models is the characteristic timescale for changes in SFR(t). This difference controls whether galaxies are assembled in bursts or in steady-state star formation, corresponding respectively to (feedback-dominated/accretion-dominated) models of galaxy formation and to (larger/smaller) confidence intervals derived from SED fitting. High-quality spectroscopy has the potential to further distinguish between these proposed models of SFR(t).