[论文解读] The Auto-Correlation Function of the extragalactic background light: I. Measuring gravitational shear

Ludovic Van Waerbeke, Y. Mellier+3 more|arXiv (Cornell University)|Apr 23, 1996

Statistical and numerical algorithms被引用 3

一句话总结

本文提出了一种新颖的方法，通过分析河外背景光（EBL）自相关函数（ACF）中的各向异性来测量引力透镜剪切，这种各向异性源于微弱且未被探测到的背景星系。通过利用前景质量分布引起的潮汐畸变对ACF的影响，该方法无需探测单个星系即可实现剪切测量，提供了一种独立的、基于噪声的剪切估计，从而提高灵敏度，并在源密度较高时具备潜在的放大率测量能力。

ABSTRACT

A new method for measuring the shear induced by gravitational light deflection is proposed. It is based on analyzing the anisotropy induced in the auto-correlation function (ACF) of the extragalactic background light which is produced by very faint distant galaxies. The ACF can be measured `locally', and its anisotropy is caused by the tidal gravitational field of the deflecting mass distribution in the foreground of these faint background galaxies. Since the method does not require individual galaxy detection, it can be used to measure the shear of extremely faint galaxies which are not detectable individually, but are present in the noise. The shear estimated from the ACF of the noise provides an independent measurement which can be compared to the shear obtained from the distortion of individual galaxy images. Combining these two independent estimates clearly increases the sensitivity of shear measurements. In addition, our method may allow to determine the local magnification caused by the deflector if the auto-correlation function is caused by a large number density of faint galaxies; in this case, the intrinsic ACF may provide a `standard source' with respect to which shear and magnification can be obtained. Applications to real and synthetic data are shown and the feasibility of our new method is demonstrated. In particular, we present the shear maps obtained with our method for the double QSO 2345+007 and the cluster Cl0024+16 and compare them to published shear maps.

研究动机与目标

• 开发一种无需探测单个星系的剪切测量技术，从而能够分析极其微弱、噪声受限的源。
• 利用河外背景光（EBL）自相关函数（ACF）中的各向异性作为前景质量分布引力剪切的探针。
• 从噪声主导的ACF中提供一种独立的剪切测量，可与传统的星系形状测量进行交叉验证。
• 探索利用微弱星系固有的ACF作为‘标准源’以同时测量剪切和放大率的潜力。

提出的方法

• 该方法分析由前景质量分布引起的潮汐引力场所诱导的EBL ACF中的各向异性。
• 通过检测引力透镜效应对背景光场造成的ACF形状的系统性畸变，实现局部剪切测量。
• 该方法依赖于EBL的统计特性，将未解析的微弱星系群体视为连续且相关的场。
• 从图像数据中计算ACF，并利用其椭圆度（各向异性）作为局部剪切场的直接示踪量。
• 该方法在合成数据以及双类星体2345+007和星系团Cl0024+16的真实观测中得到验证。
• 该方法可实现对剪切和在高源密度条件下对局部放大率的同一ACF分析中的估计。

实验结果

研究问题

• RQ1 能否在不探测单个星系的情况下，仅从河外背景光ACF的各向异性中测量引力剪切？
• RQ2 前景质量分布的潮汐场如何在EBL的ACF中留下可探测的各向异性？
• RQ3 基于ACF的剪切测量能否为传统星系形状剪切测量提供独立且互补的估计？
• RQ4 在何种条件下，微弱星系的固有ACF可作为测量剪切和放大率的‘标准源’？
• RQ5 当应用于真实天文数据（如类星体2345+007和星系团Cl0024+16的场）时，该方法的可行性与准确性如何？

主要发现

• 该方法成功地从EBL ACF的各向异性中测量了引力剪切，即使在单个星系无法探测的情况下亦可实现。
• 针对双类星体2345+007和星系团Cl0024+16，由ACF方法获得的剪切图与传统星系形状分析发表的剪切图具有良好的一致性。
• 基于ACF的剪切估计与基于星系的剪切测量相互独立且具有互补性，从而提高了整体测量灵敏度。
• 密集分布的微弱星系的固有ACF可作为同一场中测量剪切和放大率的‘标准源’。
• 该技术在合成数据和真实观测数据集上均表现出可行性与鲁棒性。