To make a power spectrum (PS) detection of the 21-cm signal from the Epoch of Reionisation (EoR), one must avoid/subtract bright foreground sources. Sources such as Fornax A present a modelling challenge due to spatial structures spanning from arc seconds up to a degree. We compare modelling with multi-scale (MS) CLEAN components to ‘shapelets’, an alternative set of basis functions. We introduce a new image-based shapelet modelling package, SHAMFI. We also introduce a new CUDA simulation code (WODEN) to generate point source, Gaussian, and shapelet components into visibilities. We test performance by modelling a simulation of Fornax A, peeling the model from simulated visibilities, and producing a residual PS. We find the shapelet method consistently subtracts large-angular-scale emission well, even when the angular resolution of the data is changed. We find that when increasing the angular resolution of the data, the MS CLEAN model worsens at large angular scales. When testing on real Murchison Widefield Array data, the expected improvement is not seen in real data because of the other dominating systematics still present. Through further simulation, we find the expected differences to be lower than obtainable through current processing pipelines. We conclude shapelets are worthwhile for subtracting extended galaxies, and may prove essential for an EoR detection in the future, once other systematics have been addressed.

中文翻译：

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使用 shapelets 对扩展源进行建模和剥离：Fornax 案例研究

为了对来自再电离时代 (EoR) 的 21 厘米信号进行功率谱 (PS) 检测，必须避免/减去明亮的前景源。由于空间结构从弧秒到一个度数，Fornax A 等源提出了建模挑战。我们将具有多尺度 (MS) CLEAN 组件的建模与“shapelets”（一组替代的基函数）进行比较。我们引入了一个新的基于图像的 shapelet 建模包 SHAMFI。我们还引入了一个新的 CUDA 模拟代码 (WODEN)，以将点源、高斯和 shapelet 组件生成到可见性中。我们通过对 Fornax A 的模拟进行建模、从模拟的可见性中剥离模型并产生残余 PS 来测试性能。我们发现 shapelet 方法始终可以很好地减去大角尺度发射，即使数据的角度分辨率发生变化。我们发现，当增加数据的角分辨率时，MS CLEAN 模型在大角尺度上会变差。在测试真实的默奇森宽场阵列数据时，没有看到预期的改进在真实数据中因为其他占主导地位的系统学仍然存在。通过进一步模拟，我们发现预期差异低于通过当前处理管道获得的差异。我们得出结论，shapelets 对于减去扩展星系是值得的，并且一旦其他系统学得到解决，它可能对未来的 EoR 检测至关重要。