It is common practice in cosmology to model large-scale structure observables as lognormal random fields, and this approach has been successfully applied in the past to the matter density and weak lensing convergence fields separately. We argue that this approach has fundamental limitations which prevent its use for jointly modelling these two fields since the lognormal distribution's shape can prevent certain correlations to be attainable. Given the need of ongoing and future large-scale structure surveys for fast joint simulations of clustering and weak lensing, we propose two ways of overcoming these limitations. The first approach slightly distorts the power spectra of the fields using one of two algorithms that minimises either the absolute or the fractional distortions. The second one is by obtaining more accurate convergence marginal distributions, for which we provide a fitting function, by integrating the lognormal density along the line of sight. The latter approach also provides a way to determine directly from theory the skewness of the convergence distribution and, therefore, the parameters for a lognormal fit. We present the public code Full-sky Lognormal Astro-fields Simulation Kit (FLASK) which can make tomographic realisations on the sphere of an arbitrary number of correlated lognormal or Gaussian random fields by applying either of the two proposed solutions, and show that it can create joint simulations of clustering and lensing with sub-per-cent accuracy over relevant angular scales and redshift ranges.
翻译:在宇宙学中,通常的做法是将大规模结构建模为可观察到的对数随机字段,这种方法过去曾成功地应用于物质密度和微弱透镜合并字段。我们争辩说,这种方法具有根本的局限性,它无法用于共同模拟这两个字段,因为对数分布的形状可以防止某些关联。鉴于当前和未来大规模结构调查对于快速联合模拟组合和微弱透镜的需要,我们建议了两种克服这些限制的方法。第一种方法是使用两种算法中的一种略微扭曲了字段的能量光谱,这两种算法可以最大限度地减少绝对偏差或分数扭曲。第二种办法是获得更准确的趋同边际分布,我们为此提供了一种适当的功能,因为对正正态分布形状的形状可以防止某些关联。后一种方法也可以直接从理论中确定聚合分布的偏差,从而确定对正态分布的快速联合模拟的参数。我们介绍了公共代码Full-skylogmanic Astroformation Kit(FLFASK),它可以使直径偏向偏差或偏差的边际分布,我们提供了一种适切的函数分布函数分布函数分布函数功能,我们提供一种适切的功能功能功能功能功能功能,在视觉上可以用来显示一个任意的直观的直径对地标标标标标标的平标的平的平的平标标标的平的平的平的平标数。