http://arxiv.org/abs/1806.11113
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.
L. Williams and J. Liesenborgs
Mon, 2 Jul 18
66/70
Comments: 13 pages, 11 figures, submitted to MNRAS
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