Clash : discovery of a bright z ≃ 6.2 dwarf galaxy quadruply lensed by MACS J0329.6-0211

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 (zl = 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 zs ≃ 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 0.9Gyr old, where the z ≃ 6.2 galaxy occupies a source-plane area of approximately 2.2kpc2. Modeling the observed spectral energy distribution using population synthesis models, we find a demagnified stellar mass of , subsolar metallicity (Z/Z 0.5), low dust content (AV 0.1mag), a demagnified star formation rate (SFR) of yr -1, and a specific SFR of 3.4Gyr-1, all consistent with the properties of local dwarf galaxies.