The role of images and priors in measuring $H_0$ from supernova Refsdal in galaxy cluster MACS J1149.5+2223
The role of images and priors in measuring $H_0$ from supernova Refsdal in galaxy cluster MACS J1149.5+2223
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图像和先验在测量星系团 MACS J1149.5 2223 中超新星 Refsdal 的 $H_0$ 中的作用
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发表时间：
2018
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通讯作者：
J. Liesenborgs
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作者：
L. Williams;J. Liesenborgs
具有测量时间延迟的多图像引力透镜系统提供了一种很有前途的一步确定H_0的方法。MACS J1149将SN Refsdal镜头转换为四分之一的S1-S4，以及另外两个广泛分离的图像SX和SY，是一个完美的候选者。如果时间延迟被固定下来，剩下的不确定性来自透镜中的质量分布。在MACS J1149中，相关透镜平面区域的质量可以受到许多多重图像的约束，分裂星系S1-S4的质量（我们表明，它与H_0相关），SX的放大率（也与H_0相关），以及对质量分布的先验假设。为了更好地理解是什么影响了H_0的测量，我们分离出与这些约束相关的不确定性。尽管通过Grale透镜反演，SX的位置恢复到~0.04 arcsec（rms ~0.26 arcsec）内，但单独使用图像产生~1000%的不确定性。固定分裂S1-S4的星系的质量将使1 sigma的不确定性降低到20%-33%，这取决于质量，而固定SX的放大率将使1 sigma的不确定性降低到35%。较小的不确定性，百分之几的顺序，是对星系和星系团质量分布的形状强加假设的结果，这可能适用于也可能不适用于合并星系团的高度非平衡环境。我们建议，如果要认为H_0的测量是可靠的，它必须得到广泛的透镜反演方法的支持。
Multiple image gravitational lensing systems with measured time delays provide a promising one-step method for determining H_0. MACS J1149, which lenses SN Refsdal into a quad S1-S4, and two other widely separated images, SX and SY, is a perfect candidate. If time delays are pinned down, the remaining uncertainty arises from the mass distribution in the lens. In MACS J1149, the mass in the relevant lens plane region can be constrained by many multiple images, the mass of the galaxy splitting S1-S4 (which, we show, is correlated with H_0), magnification of SX (also correlated with H_0), and prior assumptions on the mass distribution. To better understand what affects the measurement of H_0, we separate out the uncertainties associated with these constraints. Using images alone yields ~1000% uncertainty, despite the fact that the position of SX is recovered to within ~0.04 arcsec (rms ~0.26 arcsec) by Grale lens inversion. Fixing the mass of the galaxy that splits S1-S4 would reduce 1 sigma uncertainties to 20%-33%, depending on the mass, while fixing the magnification of SX would reduce 1 sigma uncertainties to 35%. Smaller uncertainties, of order few percent, are a consequence of imposing assumptions on the shapes of the galaxy and cluster mass distributions, which may or may not apply in a highly non-equilibrium environment of a merging cluster. We propose that if a measurement of H_0 is to be considered reliable, it must be supported by a wide range of lens inversion methods.