Joint Bayesian Estimation of Quasar Continua and the Lyα Forest Flux Probability Distribution Function
Joint Bayesian Estimation of Quasar Continua and the Lyα Forest Flux Probability Distribution Function
复制标题
连续类星体和 Lyα 森林通量概率分布函数的联合贝叶斯估计
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
K. Lee
中科院分区：
文献类型：
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作者：
A. Eilers;J. Hennawi;K. Lee
我们提出了一种新的贝叶斯算法，利用马尔可夫链蒙特卡罗采样，使我们能够同时估计高分辨率光谱集合中每个类星体的未知连续体水平，以及它们传输的 Lyα 森林通量的常见概率分布函数 (PDF)。这种全自动 PDF 调节连续谱拟合方法以线性主成分分析 (PCA) 为基础对未知类星体连续谱进行建模，并将 PCA 系数视为干扰参数。该方法允许人们估计控制星际介质（IGM）热状态的参数，例如温度-密度关系的斜率，同时以完全贝叶斯方式边缘化连续体不确定性。使用从 IGM 的简化半数值模型创建的真实模拟类星体光谱，我们表明该方法分别将底层类星体连续体恢复到 z = 3 和 z = 5 时的精度。考虑到主成分谱的数量，这与 PCA 模型本身的基本精度相当。最重要的是，我们表明，对于十个模拟高分辨率类星体光谱的集合，我们可以以 z = 3 和 z = 5 的精度对 IGM 温度-密度关系的斜率进行近乎无偏的估计。将这种方法应用于真实的类星体光谱，并与流体动力学模拟中的更真实的 IGM 模型进行比较，将能够精确测量控制 IGM 的热和宇宙学参数，尽管考虑到模型灵活性的增加，不确定性会更大。
We present a new Bayesian algorithm making use of Markov Chain Monte Carlo sampling that allows us to simultaneously estimate the unknown continuum level of each quasar in an ensemble of high-resolution spectra, as well as their common probability distribution function (PDF) for the transmitted Lyα forest flux. This fully automated PDF regulated continuum fitting method models the unknown quasar continuum with a linear principal component analysis (PCA) basis, with the PCA coefficients treated as nuisance parameters. The method allows one to estimate parameters governing the thermal state of the intergalactic medium (IGM), such as the slope of the temperature–density relation , while marginalizing out continuum uncertainties in a fully Bayesian way. Using realistic mock quasar spectra created from a simplified semi-numerical model of the IGM, we show that this method recovers the underlying quasar continua to a precision of and at z = 3 and z = 5, respectively. Given the number of principal component spectra, this is comparable to the underlying accuracy of the PCA model itself. Most importantly, we show that we can achieve a nearly unbiased estimate of the slope of the IGM temperature–density relation with a precision of at z = 3 and at z = 5, for an ensemble of ten mock high-resolution quasar spectra. Applying this method to real quasar spectra and comparing to a more realistic IGM model from hydrodynamical simulations would enable precise measurements of the thermal and cosmological parameters governing the IGM, albeit with somewhat larger uncertainties, given the increased flexibility of the model.