Parametrising galaxy morphologies is a challenging task, e.g., in shear measurements of weak lensing or investigations of galaxy evolution. The huge variety of morphologies requires an approach that is highly flexible, e.g., accounting for azimuthal structure. We revisit the method of sersiclets, where galaxy morphologies are decomposed into basis functions based on the Sersic profile. This approach is justified by the fact that the Sersic profile is the first-order Taylor expansion of any real light profile. We show that sersiclets overcome the modelling failures of shapelets. However, sersiclets implicate an unphysical relation between the steepness of the light profile and the spatial scale of azimuthal structures, which is not obeyed by real galaxy morphologies and can therefore give rise to modelling failures. Moreover, we demonstrate that sersiclets are prone to undersampling, which restricts sersiclet modelling to highly resolved galaxy images. Analysing data from the Great08 challenge, we demonstrate that sersiclets should not be used in weak-lensing studies. We conclude that although the sersiclet approach appears very promising at first glance, it suffers from conceptual and practical problems that severly limit its usefulness. The Sersic profile can be enhanced by higher-order terms in the Taylor expansion, which can drastically improve model reconstructions of galaxy images. If orthonormalised, these higher-order profiles can overcome the problems of sersiclets while preserving their mathematical justification.
Crawling the Cosmic Network: Identifying and Quantifying Filamentary Structure
We present the Smoothed Hessian Major Axis Filament Finder (SHMAFF), an algorithm that uses the eigenvectors of the Hessian matrix of the smoothed galaxy distribution to identify individual filamentary structures. Filaments are traced along the Hessian eigenvector corresponding to the largest eigenvalue, and are stopped when the axis orientation changes more rapidly than a preset threshold. In both N-body simulations and the Sloan Digital Sky Survey (SDSS) main galaxy redshift survey data, the resulting filament length distributions are approximately exponential. In the SDSS galaxy distributio…
Quantifying Environmental Effects on Galaxy Properties using Non-spherical Voids Identified from SDSS DR7
Shanghai Jiao Tong University（上海交通大学）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Chinese Academy of Sciences（中国科学院大学）
First Weak-lensing Results from "See Change": Quantifying Dark Matter in the Two Z>1.5 High-redshift Galaxy Clusters SPT-CL J2040-4451 and IDCS J1426+3508
H-ATLAS/GAMA: Quantifying the Morphological Evolution of the Galaxy Population Using Cosmic Calorimetry
利用Herschel天体物理太赫兹大面积巡天和星系与质量组装项目的结果，我们表明，对于质量大于约1.0e8太阳质量的星系，本机宇宙中51%的恒星质量密度位于早型星系中（ETG：Sersic n > 2.5），而89%的恒星质量密度产生率发生在晚型星系（LTG：Sersic n < 2.5）。从这个零红移的基准，我们已经使用了量热技术来量化的重要性的形态转变的星系在宇宙的历史。河外背景辐射包含了大爆炸以来恒星核聚变产生的全部能量。通过使用赫歇尔空间天文台的最深远红外调查和哈勃太空望远镜（HST）的深近红外/光学调查将这种背景辐射分解为单个星系，并使用来自HST图像的这些星系的Sersic指数的测量值，我们估计在宇宙历史上形成的恒星质量密度中约有83%发生在LTG中。这与现今LTG中恒星质量密度的比例之间的差异意味着在大多数恒星形成之后，LTG必须有一个主要的转变。
