A Probable z~7 Galaxy Strongly Lensed by the Rich Cluster A2218: Exploring the Dark Ages
Résumé
We discuss the observational properties of a remarkably faint triply imaged galaxy revealed in a deep z'-band Advanced Camera for Surveys observation of the lensing cluster A2218 (z=0.175). A well-constrained mass model for the cluster, which incorporates the outcome of recent Keck spectroscopic campaigns, suggests that the triple system arises via a high-redshift (z>6) source viewed at high magnification (~=25 times). Optical and infrared photometry from Hubble Space Telescope and the Keck Observatory confirms the lensing hypothesis and suggests that a significant discontinuity occurs in the spectral energy distribution within the wavelength interval 9250-9850 Å. If this break is associated with Gunn-Peterson absorption from neutral hydrogen, a redshift of 6.6