2003ApJ...598..162S

In this paper, we exploit the gravitational potential of the rich cluster A2218 as a magnifying glass. We demonstrate that the magnification due to the cluster allows us to observe distant background galaxies at a comparable level of detail to galaxies at z∼0.1. Using the Gemini Multiobject Spectrograph (GMOS) integral field unit (IFU) on Gemini North, we observed the spatially resolved [O II] λ3727 emission line spectrum for a lensed disk galaxy at z=1.034. Using a detailed model for the cluster mass distribution, we are able to correct for the lensing by the cluster and reconstruct the source morphology. We find that the overall magnification is a factor of 4.92±0.15, and the rest-frame absolute I-band magnitude is M^rest_I=-22.4±0.2, where the error bars include conservative estimates of the uncertainty in the source-plane reconstruction. The inclination-corrected circular velocity is 206±18 km/s. The galaxy lies very close to the mean Tully-Fisher relation of present-day spirals. Although our results are based on a single object, they demonstrate that gravitational lensing can be viably used to make detailed studies of the evolution of the structure of distant field galaxies.