2008ApJ...678..647B

Using Hubble Space Telescope (HST) and Spitzer IRAC imaging, we report the discovery of a very bright strongly lensed Lyman break galaxy (LBG) candidate at z∼7.6 in the field of the massive galaxy cluster Abell 1689 (z=0.18). The galaxy candidate, which we refer to as A1689-zD1, shows a strong z₈₅₀-J₁₁₀ break of at least 2.2 mag and is completely undetected (<1 σ) in HST Advanced Camera for Surveys (ACS) g₄₇₅, r₆₂₅, i₇₇₅, and z₈₅₀data. These properties, combined with the very blue J₁₁₀-H₁₆₀ and H₁₆₀-[4.5 µm] colors, are exactly the properties of an z∼7.6 LBG, and can only be reasonably fit by a star-forming galaxy at z=7.6±0.4 (χ²_ν=1.1). Attempts to reproduce these properties with a model galaxy at z<4 yield particularly poor fits (χ²_ν≥25). A1689-zD1 has an observed (lensed) magnitude of 24.7 AB (8 σ) in the NICMOS H₁₆₀ band and is ∼1.3 mag brighter than the brightest known z₈₅₀-dropout galaxy. When corrected for the cluster magnification of ∼9.3 at z∼7.6, the candidate has an intrinsic magnitude of H₁₆₀=27.1 AB, or about an L_* galaxy at z∼7.6. The source-plane deprojection shows that the star formation is occurring in compact knots of size ≲300 pc. The best-fit stellar population synthesis models yield a median redshift of 7.6, stellar masses (1.6-3.9)x10⁹ M_☉, stellar ages 45-320 Myr, star formation rates ≲7.6 M_☉/yr, and low reddening with A_V≤0.3. These properties are generally similar to those of LBGs found at z∼5-6. The inferred stellar ages suggest a formation redshift of z∼8-10 (t≲0.63 Gyr). A1689-zD1 is the brightest observed, highly reliable z>7.0 galaxy candidate found to date.