Mass-sheet degeneracy, power-law models and external convergence: Impact on the determination of the Hubble constant from gravitational lensing
Mass-sheet degeneracy, power-law models and external convergence: Impact on the determination of the Hubble constant from gravitational lensing
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质量片简并性、幂律模型和外部会聚：对通过引力透镜确定哈勃常数的影响
DOI：
10.1051/0004-6361/201321882
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发表时间：
2013
影响因子：
6.5
通讯作者：
D. Sluse
中科院分区：
文献类型：
--
作者：
P. Schneider;D. Sluse
强引力透镜系统中的光传播时间差允许独立确定哈勃常数。该方法已成功应用于多种镜头系统。然而，形式上最精确的测量与最近从普朗克卫星确定的空间平坦六参数 ΛCDM 宇宙学的 H0 存在矛盾。我们重新考虑了该方法在透镜星系质量分布方面的不确定性，并表明形式精度依赖于质量分布是完美幂律的假设。简单的分析论证和数值实验表明，即使观察到精致的爱因斯坦环，类似质量片的变换在选择质量分布方面也具有很大的自由度。此外，透镜环境的表征并没有打破与外在会聚物理上没有联系的简并性。我们提出了一个说明性示例，其中复合（重子 + 暗物质）透镜的多种成像特性可以通过具有相同速度色散的幂律模型非常好地再现，但哈勃常数的预测偏差约 20%。因此，我们得出的结论是，在当前的 H0 透镜测量中，参数化模型之间简并的影响被低估了，需要仔细重新考虑。
The light travel time differences in strong gravitational lensing systems allows an independent determination of the Hubble constant. This method has been successfully applied to several lens systems. The formally most precise measurements are, however, in tension with the recent determination ofH0from thePlancksatellite for a spatially flat six-parameters ΛCDM cosmology. We reconsider the uncertainties of the method, concerning the mass profile of the lens galaxies, and show that the formal precision relies on the assumption that the mass profile is a perfect power law. Simple analytical arguments and numerical experiments reveal that mass-sheet like transformations yield significant freedom in choosing the mass profile, even when exquisite Einstein rings are observed. Furthermore, the characterization of the environment of the lens does not break that degeneracy which is not physically linked to extrinsic convergence. We present an illustrative example where the multiple imaging properties of a composite (baryons + dark matter) lens can be extremely well reproduced by a power-law model having the same velocity dispersion, but with predictions for the Hubble constant that deviate by ~20%. Hence we conclude that the impact of degeneracies between parametrized models have been underestimated in currentH0measurements from lensing, and need to be carefully reconsidered.