2012ApJ...747L...9Z

We report the discovery of a z_phot= 6.18^+0.05_- 0.07_(95% confidence level) dwarf galaxy, lensed into four images by the galaxy cluster MACS J0329.6-0211 (z_l= 0.45). The galaxy is observed as a high-redshift dropout in HST/ACS/WFC3 CLASH and Spitzer/IRAC imaging. Its redshift is securely determined due to a clear detection of the Lyman break in the 18-band photometry, making this galaxy one of the highest-redshift multiply lensed objects known to date with an observed magnitude of F125W =24.00±0.04 AB mag for its most magnified image. We also present the first strong-lensing analysis of this cluster uncovering 15 additional multiply imaged candidates of five lower-redshift sources spanning the range z_s≃ 2-4. The mass model independently supports the high photometric redshift and reveals magnifications of 11.6^+8.9_- 4.1_, 17.6^+6.2_- 3.9_, 3.9^+3.0_- 1.7_, and 3.7^+1.3_- 0.2_, respectively, for the four images of the high-redshift galaxy. By delensing the most magnified image we construct an image of the source with a physical resolution of ∼200 pc when the universe was ∼0.9 Gyr old, where the z ≃ 6.2 galaxy occupies a source-plane area of approximately 2.2 kpc². Modeling the observed spectral energy distribution using population synthesis models, we find a demagnified stellar mass of ∼10⁹M_☉, subsolar metallicity (Z/Z_☉∼ 0.5), low dust content (A_V∼ 0.1 mag), a demagnified star formation rate (SFR) of ∼ 3.2 M_☉/yr, and a specific SFR of ∼3.4/Gyr, all consistent with the properties of local dwarf galaxies.