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arXiv 2104.08883astro-ph.COgr-qc
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强引力透镜中的视线效应

Line-of-sight effects in strong gravitational lensing

Pierre Fleury, Julien Larena, Jean-Philippe Uzan

摘要:

虽然大多数强引力透镜系统可以粗略地由源和观察者之间的单个大质量物体建模,但在细节上,光路附近的所有结构都有助于观察到的图像。这些额外的贡献,称为视线效应,在实践中是不可忽略的。本文提出了一个新的理论框架来模拟视线效应,以及在弱透镜和强透镜界面上非常有前途的应用。我们的方法依赖于主透镜近似,其中一个偏转器被视为主透镜,而其他被视为扰动。由此产生的框架是技术上更简单的处理比多平面透镜形式主义,同时允许一个一致的任何亚临界扰动模型。特别是,它不限于通常的外部收敛和外部剪切参数化。作为第一个应用程序,我们确定了一个特定的概念,视线剪切,不退化的椭圆率的主透镜,从而可以从强透镜图像中提取。这一结果支持并改进了最近提出的爱因斯坦环可能是宇宙剪切的强大探针的建议。作为第二个应用程序,我们调查的扭曲的强透镜临界曲线下的视线的影响,更特别的是它们的相关性在整个天空。我们发现,这种相关性不仅可以用来探测宇宙的大尺度结构,而且可以用来探测强透镜的暗物质晕轮廓。这最后一种可能性将是一个关键的资产,以提高通过时间延迟宇宙学测量哈勃-勒梅特常数的准确性。

英文摘要:

While most strong-gravitational-lensing systems may be roughly modelled by a single massive object between the source and the observer, in the details all the structures near the light path contribute to the observed images. These additional contributions, known as line-of-sight effects, are non-negligible in practice. This article proposes a new theoretical framework to model the line-of-sight effects, together with very promising applications at the interface of weak and strong lensing. Our approach relies on the dominant-lens approximation, where one deflector is treated as the main lens while the others are treated as perturbations. The resulting framework is technically simpler to handle than the multi-plane lensing formalism, while allowing one to consistently model any sub-critical perturbation. In particular, it is not limited to the usual external-convergence and external-shear parameterisation. As a first application, we identify a specific notion of line-of-sight shear that is not degenerate with the ellipticity of the main lens, and which could thus be extracted from strong-lensing images. This result supports and improves the recent proposal that Einstein rings might be powerful probes of cosmic shear. As a second application, we investigate the distortions of strong-lensing critical curves under line-of-sight effects, and more particularly their correlations across the sky. We find that such correlations may be used to probe, not only the large-scale structure of the Universe, but also the dark-matter halo profiles of strong lenses. This last possibility would be a key asset to improve the accuracy of the measurement of the Hubble-Lemaître constant via time-delay cosmography.

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