A bias in cosmic shear from galaxy selection: results from ray-tracing simulations
A bias in cosmic shear from galaxy selection: results from ray-tracing simulations
复制标题
DOI：
10.1051/0004-6361/201015850
复制
发表时间：
2010-09
影响因子：
6.5
通讯作者：
J. Hartlap;S. Hilbert;P. Schneider;H. Hildebrandt
中科院分区：
文献类型：
--
作者：
J. Hartlap;S. Hilbert;P. Schneider;H. Hildebrandt
目标。我们确定和研究一个以前未知的宇宙剪切测量系统的影响，所造成的选择用于形状测量的星系，特别是拒绝密切（混合）星系对。方法.我们使用基于千禧年模拟的射线跟踪模拟和星系形成的半分析模型来创建逼真的星系目录。从这些，我们量化的剪切相关函数的偏差，通过比较从星系目录与不删除的密切对。似然分析被用来量化宇宙学参数估计的变化。结果对近邻天体的过滤：（a）改变了用于相关函数测量的星系的红移分布;（B）将背景中源的数量密度与前景中的密度场相关联。这导致了相关函数的几个百分比的尺度依赖性偏差，转化为类似幅度的宇宙学参数的偏差。这使得这种新的系统效应对即将进行的和计划中的宇宙切变调查可能有害。作为一种补救措施，我们提出并测试了一个加权方案，可以显着减少偏见。
Aims. We identify and study a previously unknown systematic effect on cosmic shear measurements, caused by the selection of galaxies used for shape measurement, in particular the rejection of close (blended) galaxy pairs. Methods. We use ray-tracing simulations based on the Millennium Simulation and a semi-analytical model of galaxy formation to create realistic galaxy catalogues. From these, we quantify the bias in the shear correlation functions by comparing measurements made from galaxy catalogues with and without removal of close pairs. A likelihood analysis is used to quantify the resulting shift in estimates of cosmological parameters. Results. The filtering of objects with close neighbours: (a) changes the redshift distribution of the galaxies used for correlation function measurements; and (b) correlates the number density of sources in the background with the density field in the foreground. This leads to a scale-dependent bias of the correlation function of several percent, translating into biases of cosmological parameters of similar amplitude. This makes this new systematic effect potentially harmful for upcoming and planned cosmic shear surveys. As a remedy, we propose and test a weighting scheme that can significantly reduce the bias.