Spitzer and Hubble Space Telescope Constraints on the Physical Properties of the z ~ 7 Galaxy Strongly Lensed by A2218
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We report the detection of a z ∼ 7 galaxy strongly lensed by the massive galaxy cluster A2218 (z = 0.175) at 3.6 and 4.5 μm using the Spitzer Space Telescope and at 1.1 μm 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 Lyα 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 ∼50 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 z ∼ 3-4, the stellar mass is an order of magnitude smaller (∼10 9 M ⊙ ), but the specific star formation rate (star formation rate/M/ star ) is similarly large (>10 -9 yr -1 ), indicating equally vigorous star-forming activity.
author list (cited authors)
Egami, E., Kneib, J., Rieke, G. H., Ellis, R. S., Richard, J., Rigby, J., ... Pérez-González, P. G.