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Lines of sight with multiple, projected, cluster-scale halos have high total masses and complex lens plane interactions that can boost the area of magnification, or etendue, making detection of faint background sources more likely than elsewhere. To identify these new compound cosmic telescopes, we have found lines-of-sight with the highest integrated mass densities, as traced by the projected concentrations of Luminous Red Galaxies (LRGs). We use 1151 MMT Hectospec spectra to derive preliminary magnification maps for two such lines of sight with total mass exceeding ~ 3 x 10$^{15}$ Msun -- J0850+3604 (0850) and J1306+4632 (1306). We identify 2-3 group- and cluster-scale halos in each beam over 0.1 < z < 0.7, all of which are well-traced by LRGs. In Subaru Suprime-Cam imaging of beam 0850, we discover serendipitously a candidate multiply-imaged V-dropout source at z = 5.03, whose location is consistent with the critical curves for a source plane of $z_s$ = 5.03 predicted by our mass model. Incorporating the position of the candidate multiply-imaged galaxy as a constraint on the critical curve location in 0850 narrows the 68% confidence band on lens plane area with mu > 10 for a source plane of $z_s$ = 10 to [1.8, 4.2] square arcminutes, comparable to that of MACS 0717+3745 and El Gordo, two of the most powerful known single cluster lenses. The 68% confidence intervals on the lens plane area with mu > 10 for 1306 are [2.3, 6.7] square arcminutes. The significant lensing power of our beams makes them powerful probes of reionization and galaxy formation in the early Universe.
We investigate the relationship between the halo mass, M_200, and concentration, c, for a sample of 26 group- and cluster-scale strong gravitational lenses. In contrast with previous results, we find that these systems are only ~ 0.1 dex more over-co
The gravitational potential of clusters of galaxies acts as a cosmic telescope allowing us to find and study galaxies at fainter limits than otherwise possible and thus probe closer to the epoch of formation of the first galaxies. We use the Bullet C
Current and future generations of intensity mapping surveys promise dramatic improvements in our understanding of galaxy evolution and large-scale structure. An intensity map provides a census of the cumulative emission from all galaxies in a given r
We examine the latest data on the cluster MACSJ0717.5+3745 from the Hubble Frontier Fields campaign. The critically lensed area is the largest known of any lens and very irregular making it a challenge for parametric modelling. Using our Free-Form me
The radial escape-velocity profile of galaxy clusters has been suggested to be a promising and competitive tool for constraining mass profiles and cosmological parameters in an accelerating universe. However, the observed line-of-sight escape profile