CFHTLS深度巡天PSF修正改进

发布时间：2018-04-22 12:03

本文选题：CFHTLS + PSF　；参考：《上海师范大学》2013年硕士论文

【摘要】：理论和观测结果对比表明：宇宙中绝大部分物质是不发光的，且这些物质无法使用光学观测方法观测。通过对引力透镜的研究可以得到透镜天体的引力场的物质分布情况。当前弱引力透镜研究的主流方法是宇宙剪切由宇宙大尺度结构所引起的弱引力透镜现象，其精度主要取决于对星系形状的精确测量。点扩散函数（Point Spread Function，简称PSF）是一个描述点源（例如恒星）变成面源的函数，是天体物理研究必须考虑的问题。遥远天体发出的光在到达望远镜终端CCD的过程中，会受到大气抖动、大气湍流、大气视宁度（seeing）和望远镜自身扭曲等因素的影响，最终使得该遥远天体在CCD上的成像发生扭曲形变。通过寻找一个合适的PSF能够修正这些干扰因素对成像的影响，从而能够精确测量星系的椭率，进而提高宇宙剪切对宇宙学参数限定的精度。本文研究的数据源自加拿大天文数据中心（CADC）的CFHTLS（Canada-France-Hawaii Telescope LegacySurvey）深度巡天第六次释放r′波段的D1、D2、D3和D4这4个天区最好视宁度25%的数据。本文以CFHTLS Deep巡天第二天区为例展开论述（简称D2-r′-25）。通过对点扩散函数的修正改进来提高CFHTLS望远镜深度巡天星系成像椭率的测量精度。本文通过两种方法来提高点扩散函数(PSF)的修正改进：第一种PSF修正的方法是整体拟合，即以一个平方度天区的图片为单位进行整体的拟合，先对高质量恒星样本做PSF修正，然后将恒星的PSF拟合修正推广到星系的PSF拟合修正。第二种方法将一个平方度天区的图片按PSF图形情况手动分割成若干块（本文分割成4块），然后对每一小块天区采用低阶拟合。两种PSF拟合修正的区别在于：对整体拟合而言，可能某些地方出现过度拟合，，某些地方出现拟合不够；对分割后每个子天区采用低阶拟合而言，能够更好的控制拟合函数的选取和拟合程度的控制等具体情况。通过比较这两种拟合结果，来确定CFHTLS Deep的PSF修正方式，并计算星系的剪切两点相关函数。
[Abstract]:The comparison of theoretical and observational results shows that the vast majority of matter in the universe is not luminous, and these materials cannot be observed by optical observation method. Through the study of gravitational lensing, the mass distribution of gravitational field of lens celestial body can be obtained. At present, the main method in the study of weak gravitational lensing is the phenomenon of weak gravitational lensing caused by the cosmic large scale structure. Its accuracy mainly depends on the accurate measurement of the shape of galaxies. Point Spread function (PSF) is a function that describes the point source (such as a star) becoming a point source, which must be considered in the study of astrophysics. The light emitted by distant celestial bodies is affected by atmospheric jitter, atmospheric turbulence, atmospheric visibility and distortion of the telescope itself as it reaches the telescope terminal CCD. Finally, the image of the distant object on the CCD is distorted and deformed. By looking for a suitable PSF, the influence of these interference factors on imaging can be corrected, thus the ellipticity of galaxies can be accurately measured, and the precision of cosmic shear defining cosmological parameters can be improved. The data in this paper are derived from the CFHTLS(Canada-France-Hawaii Telescope Legacy Survey of the Canadian Astronomical data Center (CADC) for the sixth time to release the data of D1D2D3 and D4 in the R 'band with the best visibility of 25%. This paper takes the second day area of CFHTLS Deep survey as an example. By modifying the point diffusion function, the measurement accuracy of the ellipsometry of the CFHTLS telescope's depth survey galaxy imaging is improved. In this paper, the point diffusion function (PSF) is improved by two methods: the first method of PSF correction is global fitting, that is, the whole fitting is based on a square sky image, and the high mass star sample is first modified by PSF. Then the PSF fitting correction of stars is extended to the PSF fitting correction of galaxies. In the second method, a square area image is manually divided into several blocks according to the PSF graph (this paper divides into 4 blocks, and then uses low-order fitting for each small area of sky. The difference between the two PSF fitting amendments lies in the fact that, for the whole fitting, there may be over-fitting in some places and insufficient fitting in some places; for each sub-area after segmentation, low-order fitting is used. It can better control the selection of fitting function and the control of fitting degree. By comparing these two fitting results, the PSF correction method of CFHTLS Deep is determined, and the two-point correlation function of galaxy shear is calculated.
【学位授予单位】：上海师范大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：P14

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