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arXiv 2212.09797astro-ph.COastro-ph.GA
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21cmfish: 用于从宇宙21厘米信号进行快速参数预测的Fisher矩阵框架

21cmfish: Fisher-matrix framework for fast parameter forecasts from the cosmic 21-cm signal

Charlotte A. Mason, Julian B. Muñoz, Bradley Greig, Andrei Mesinger, Jaehong Park

AI总结:

本研究提出面向半数值模拟21cmFAST的Fisher矩阵工具21cmfish,可高效完成21厘米信号参数预测,计算量比MCMC方法低约10⁴倍;基于10参数空间的HERA预测显示,X射线参数可达亚百分比精度,恒星相关参数约束精度约10%。

摘要:

来自早期宇宙中性氢的21厘米信号将为我们提供关于第一代恒星和星系的前所未有的信息。然而,提取这些信息需要考虑诸多未知的天体物理过程。半数值模拟是探索上述过程广阔参数空间的关键工具。这类模拟采用 excursion set(漫游集)理论和微扰理论等近似技术来模拟星系际介质的三维演化,其计算成本仅为流体动力学和/或辐射转移模拟的一小部分。尽管如此,探索第一代星系的庞大参数空间在计算上仍然成本高昂。\n本文介绍了21cmfish,这是一款针对半数值模拟程序21cmFAST的Fisher矩阵封装工具。21cmfish假设后验分布为多元高斯分布,可实现高效的参数预测,能够扩展到比MCMC(马尔可夫链蒙特卡洛)方法高得多的维度。我们的方法生成的参数不确定度预测与既往MCMC分析结果相当,但所需的模拟次数减少了约10⁴倍,这为添加新物理机制和/或额外参数的分析原型设计提供了快速途径。\n我们利用迄今最大的天体物理参数空间(包含10个自由参数,涵盖第二代(Population II)和第三代(Population III)恒星形成过程)对HERA(氢再电离时代阵列)开展了预测研究。结果发现,第一代星系的X射线参数可测量至亚百分比精度;尽管存在高度简并,第二代和第三代星系的恒星-晕质量关系与电离光子逃逸分数(对数物理量)可被约束至约10%的精度。通过主成分分析我们发现,HERA对第二代星系的电离逃逸分数与恒星-晕质量分数的乘积最为敏感。

英文摘要:

The 21-cm signal from neutral hydrogen in the early universe will provide unprecedented information about the first stars and galaxies. Extracting this information, however, requires accounting for many unknown astrophysical processes. Semi-numerical simulations are key for exploring the vast parameter space of said processes. These simulations use approximate techniques such as excursion-set and perturbation theory to model the 3D evolution of the intergalactic medium, at a fraction of the computational cost of hydrodynamic and/or radiative transfer simulations. However, exploring the enormous parameter space of the first galaxies can still be computationally expensive. Here we introduce 21cmfish, a Fisher-matrix wrapper for the semi-numerical simulation 21cmFAST. 21cmfish facilitates efficient parameter forecasts, scaling to significantly higher dimensionalities than MCMC approaches, assuming a multi-variate Gaussian posterior. Our method produces comparable parameter uncertainty forecasts to previous MCMC analyses but requires ~10$^4$x fewer simulations. This enables a rapid way to prototype analyses adding new physics and/or additional parameters. We carry out a forecast for HERA using the largest astrophysical parameter space to-date, with 10 free parameters, spanning both population II and III star formation. We find X-ray parameters for the first galaxies could be measured to sub-percent precision, and, though they are highly degenerate, the stellar-to-halo mass relation and ionizing photon escape fraction for population II and III galaxies can be constrained to ~10% precision (logarithmic quantities). Using a principal component analysis we find HERA is most sensitive to the product of the ionizing escape fraction and the stellar-to-halo mass fraction for population II galaxies.

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