We present a framework and an open-source python toolkit to analyse the 2-point statistics of 3D fluctuations in the context of HI intensity maps using the multipole expansion formalism. We include simulations of the cosmological HI signal using N-body and log-normal methods, foregrounds and their removal, as well as instrumental effects. Using these simulations and analytical modelling, we investigate the impact of foreground cleaning and the instrumental beam on the power spectrum multipoles as well as on the Fourier space clustering wedges. We find that both the instrumental beam and the foreground removal can produce a quadrupole (and a hexadecapole) signal, and demonstrate the importance of controlling and accurately modelling these effects for precision radio cosmology. We conclude that these effects can be modelled with reasonable accuracy using our multipole expansion technique. We also perform an MCMC analysis to showcase the effect of foreground cleaning on the estimation of the HI abundance and bias parameters. The accompanying python toolkit is available at this https URL, and includes an interactive suite of examples to aid new users.

中文翻译：

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Hi 强度映射实验的多极扩展：模拟和建模

我们提出了一个框架和一个开源 python 工具包，以使用多极扩展形式来分析 HI 强度图背景下 3D 波动的 2 点统计数据。我们包括使用 N 体和对数正态方法、前景及其去除以及仪器效应对宇宙学 HI 信号的模拟。使用这些模拟和分析建模，我们研究了前景清洁和仪器光束对功率谱多极子以及傅立叶空间聚类楔的影响。我们发现仪器光束和前景去除都可以产生四极（和十六极）信号，并证明了控制和准确模拟这些效应对精密射电宇宙学的重要性。我们得出结论，可以使用我们的多极扩展技术以合理的精度对这些影响进行建模。我们还进行了 MCMC 分析，以展示前景清理对 HI 丰度和偏差参数估计的影响。随附的 Python 工具包可在此 https URL 上获得，其中包含一个交互式示例套件以帮助新用户。