标题： 解析截面用于亚结构透镜效应 显示英文标题

标题： Analytic Cross Sections for Substructure Lensing

摘要： 强引力透镜系统的图像放大率对透镜势中的小质量团块很敏感；这一效应已被用来推断星系暗物质晕中亚结构的数量。 我研究了亚结构透镜理论以识别重要的普遍特征，并计算解析截面，这将有助于进一步的理论研究。 我表明，视线上的任何地方出现的小团块问题都可以映射到一个简单汇聚和剪切场中小团块的等效问题；因此，在计算中处理任意红移处的小团块并不困难。 对于建模为奇异等温球（SIS）的小团块，我导出了简单解析估计的放大扰动强度截面。 这些结果得出两个有趣的概念点。 首先，具有正奇偶性的透镜图像总是被SIS小团块增亮；负奇偶性的图像可以被增亮，但更可能被变暗。 其次，这些小团块不需要位于透镜星系内部；它们可以在红移上移动几分之一，仍然会有显著的透镜效应。 孤立的小晕在等级结构形成模型中被认为是常见的，但目前还不清楚它们是否足够丰富，以影响对亚结构透镜现象的解释。 显示英文摘要

摘要： The magnifications of the images in a strong gravitational lens system are sensitive to small mass clumps in the lens potential; this effect has been used to infer the amount of substructure in galaxy dark matter halos. I study the theory of substructure lensing to identify important general features, and to compute analytic cross sections that will facilitate further theoretical studies. I show that the problem of a clump anywhere along the line of sight to a lens can be mapped onto an equivalent problem of a clump in a simple convergence and shear field; clumps at arbitrary redshifts are therefore not hard to handle in calculations. For clumps modeled as singular isothermal spheres (SIS), I derive simple analytic estimates of the cross section for magnification perturbations of a given strength. The results yield two interesting conceptual points. First, lensed images with positive parity are always made brighter by SIS clumps; images with negative parity can be brightened but are much more likely to be dimmed. Second, the clumps need not lie within the lens galaxy; they can be moved in redshift by several tenths and still have a significant lensing effect. Isolated small halos are expected to be common in hierarchical structure formation models, but it is not yet known whether they are abundant enough compared with clumps inside lens galaxies to affect the interpretation of substructure lensing.