A Faint Star-forming System Viewed through the Lensing Cluster Abell 2218:First Light at z ≃ 5.6?

We discuss the physical nature of a remarkably faint pair of Lyα-emitting images discovered close to the giant cD galaxy in the lensing cluster Abell 2218 (z = 0.18) during a systematic survey for highly magnified star-forming galaxies beyond z = 5. A well-constrained mass model suggests the pair arises via a gravitationally lensed source viewed at high magnification. Keck spectroscopy confirms the lensing hypothesis and implies that the unlensed source is a very faint (I ~ 30), compact (<150 h pc), and isolated object at z = 5.576 whose optical emission is substantially contained within the Lyα emission line; no stellar continuum is detectable. The available data suggest the source is a promising candidate for an isolated ~106 M☉ system seen producing its first generation of stars close to the epoch of reionization.