$H_0$的星系透镜测定：椭圆+剪切模拟假设的影响
Galaxy-lens determination of $H_0$: the effect of the ellipse+shear modeling assumption
摘要：
星系透镜体经常被模拟为一个椭圆形的质量分布与外部剪切和等温球，以考虑二级和视线星系。有统计学证据表明，观察到的四边形中有一部分与这些假设不一致，并且需要相对于光对质量的偶极贡献。简化关于质量分布形状的假设可能会导致不正确的参数恢复，如$H_0$。我们创建了几个测试的合成四人口与不同的偏差从椭圆形，然后将它们与椭圆+剪切模型，并测量恢复值的$H_0$。不包括运动学约束。我们执行两种类型的拟合--一种使用单个点源，另一种使用模拟扩展源的源阵列。我们进行了两个模型之间的比较，我们的模拟四边形和观察到的人口。这些比较的一个结果是文献中尚未提到的统计不一致性：观察到的四边形相对于晶状体中心的像距比似乎比合成或模拟四边形跨越更宽的范围。考虑到这种差异，我们的模拟人群可能会导致$H_0$ $\sim10\%$的偏倚。
英文摘要：
Galaxy lenses are frequently modeled as an elliptical mass distribution with external shear and isothermal spheres to account for secondary and line-of-sight galaxies. There is statistical evidence that some fraction of observed quads are inconsistent with these assumptions, and require a dipole-like contribution to the mass with respect to the light. Simplifying assumptions about the shape of mass distributions can lead to the incorrect recovery of parameters such as $H_0$. We create several tests of synthetic quad populations with different deviations from an elliptical shape, then fit them with an ellipse+shear model, and measure the recovered values of $H_0$. Kinematic constraints are not included. We perform two types of fittings -- one with a single point source and one with an array of sources emulating an extended source. We carry out two model-free comparisons between our mock quads and the observed population. One result of these comparisons is a statistical inconsistency not yet mentioned in the literature: the image distance ratios with respect to the lens center of observed quads appear to span a much wider range than those of synthetic or simulated quads. Bearing this discrepancy in mind, our mock populations can result in biases on $H_0$ $\sim10\%$.
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