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 (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 0.9Gyr 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 (A_V 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.