0 Assigned ID: 651 ----- Attempting Submission 1 (Fri Mar 06 18:41:37 GMT 2020) ----- HST Phase I Proposal 651 successfully submitted. Receipt: # 651-2 ----- Attempting Submission 3 (Fri Mar 06 22:21:51 GMT 2020) ----- We propose to measure the Hubble constant from time delays in three quasars, strongly lensed by clusters of galaxies. Recent measurements of the H_0 show increasing tension between measurements based on the local distance ladder, and those originating from the cosmic microwave background radiation. The discrepancy between these increasingly precise measurements suggests that the systematics of one or both of these measurements are underestimated, or alternatively, calls for new physics. A third method to measure H_0 is from its scaling with the delay between the arrival times of two or more images of a strongly-lensed variable source (Refsdal 1964), and has been implemented in samples of galaxy-lensed quasars. We propose to explore the feasibility of deriving precise H_0 measurements from cluster-lensed quasars. Quasars lensed by clusters are rare; to date, only five large-separation cluster-lensed quasars have been reported. The longer time delays in cluster-lensed quasars mean that the fractional uncertainty in their time delay measurement is at the few percent level. The large separation reduces systematics from microlensing and baryonic physics. On the other hand, the complexity of the cluster lens is likely to make this measurement more difficult. A careful analysis of systematic and statistical sources of uncertainty is called for; this measurement requires Hubble quality data, which is available for three of the five systems. If successful, this study will establish best practices, map and quantify the sources of error due to lens modeling, and pave the road for utilizing new targets that will be discovered in large ongoing and future surveys. Our collaboration has extensive experience with interpreting and modeling lensing clusters (e.g., Dahle et al. 2013, ApJ, 773, 146; Sharon et al. 2012, ApJ, 746, 161; Gladders et al. 2013, ApJ, 764, 177, Bayliss et al. 2011, ApJS, 193, 8, Sharon et al. 2020 , ApJS 247, 12). Dr. Sharon is an expert on strong lens modelling, with extensive experience from building lens models based on multi-band HST imaging. She has worked extensively on several of the previously known lens systems where quasars are lensed by galaxy clusters: The first large separation lensed quasar SDSSJ1004 (Sharon et al. 2005, ApJ, 629, L73), and the sextuply lensed SDSSJ2222 which was discovered by our collaboration (Dahle et al. 2013, ApJ, 773, 146; Sharon et al. 2017, ApJ, 835, 5). Dr. Sharon was PI of a HST program (#13337) "Resolving the Cluster-Lensed Sextuple Quasar SDSSJ2222+2745", also including Co-Is Gladders, Bayliss, and Dahle. This work has led to the following publications so far (several more are currently in preparation): * Sharon et al. (2017, ApJ, 835, 5): "Lens Model and Time Delay Predictions for the Sextuply Lensed Quasar SDSS J2222+2745". * Bayliss et al. (2017, ApJ, 845, L14): "Spatially Resolved Patchy Lyman-alpha Emission within the Central Kiloparsec of a Strongly Lensed Quasar Host Galaxy at z = 2.8". Dr. Dahle has led a successful photometric monitoring campaign to measure time delays for the cluster-lensed quasar SDSSJ2222+2745 (the first two time delays were published in Dahle et al. 2015, ApJ, 813, 67) and is currently leading a similar effort for SDSSJ0909+4449 and SDSSJ1326+4806, using the 2.56m Nordic Optical Telescope. Dr. Mahler is an expert in strong lensing with ample experience in modeling the HFF clusters (Mahler et al. 2018), is part of the LENSTOOL development team, and is an expert in MUSE IFU spectroscopy analysis. Dr. Gladders is a galaxy cluster and strong lensing expert, with extensive experience in data handling and analysis (spectroscopic and photometric) and a publication record of currently 196 refereed papers. Gladders has built two instruments for the Magellan telescopes, and is an active user of many of the world's largest telescopes, and HST. Gladders' research group at the University of Chicago is focused on exploiting emerging galaxy cluster and strong lensing samples to answer questions about galaxy and structure formation and evolution. Large Scale Structure of the Universe 0 Regular false true false false false SUPPORTED