Spitzer and Hubble Space Telescope constraints on the physical properties of the z similar to 7 galaxy strongly lensed by A2218

We report the detection of a z similar to 7 galaxy strongly lensed by the massive galaxy cluster A2218 (z = 0.175) at 3.6 and 4.5 mum using the Spitzer Space Telescope and at 1.1 mum using the Hubble Space Telescope. The new data indicate a refined photometric redshift in the range of 6.6-6.8 depending on the presence of Lyalpha emission. The spectral energy distribution is consistent with having a significant Balmer break, suggesting that the galaxy is in the poststarburst stage with an age of at least similar to50 Myr and quite possibly a few hundred million years. This suggests the possibility that a mature stellar population is already in place at such a high redshift. Compared with typical Lyman break galaxies at, the stellar mass is an order of magnitude smaller (similar to10(9) M-circle dot), but the specific star formation rate (star formation rate/M-star) is similarly large (>10(-9) yr(-1)), indicating equally vigorous star-forming activity.