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Galaxy-cluster gravitational lenses enable the study of faint galaxies evenat large lookback times, and, recently, time-delay constraints on the Hubbleconstant. There have been few tests, however, of lens model predictionsadjacent to the critical curve (<8") where the magnification is greatest. In acompanion paper, we use the GLAFIC lens model to constrain the Balmer L-sigmarelation for HII regions in a galaxy at redshift z=1.49 strongly lensed by theMACS J1149 galaxy cluster. Here we perform a detailed comparison between thepredictions of ten cluster lens models which employ multiple modelingassumptions with our measurements of 11 magnified giant HII regions. We findthat that the models predict magnifications an average factor of 6.2 smaller, a2-sigma tension, than that inferred from the HII regions under the assumptionthat they follow the low-redshift L-sigma relation. To evaluate the possibilitythat the lens model magnifications are strongly biased, we next consider theflux ratios among knots in three images of Sp1149, and find that these areconsistent with model predictions. Moreover, while the mass-sheet degeneracycould in principle account for a factor of ~6 discrepancy in magnification, thevalue of H0 inferred from SN Refsdal's time delay would become implausiblysmall. We conclude that the lens models are not likely to be highly biased, andthat instead the HII regions in Sp1149 are substantially more luminous than thelow-redshift Balmer L-sigma relation predicts.

Sp1149 II: Spectroscopy of HII Regions Near the Critical Curve of MACS J1149 and Cluster Lens Models