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 Ly alpha -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 similar to 30), compact (<150 h(65)(-1) pc), and isolated object at z = 5.576 whose optical emission is substantially contained within the Ly alpha emission line; no stellar continuum is detectable. The available data suggest the source is a promising candidate for an isolated similar to 10(6) M-. system seen producing its first generation of stars close to the epoch of reionization.