CLASH: Discovery of a Bright z~6.2 Dwarf Galaxy Quadruply Lensed by MACS J0329.6-0211
Abstract
We report the discovery of a zphot=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=24.000.04 AB mag for its highest-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. With this we construct a source image 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 ~109 Msun, subsolar metallicity (Z/Zsun~0.5), low dust content (AV~0.1 mag), a demagnified star formation rate (SFR) of ~3.2 Msun yr-1, and a specific SFR of ~3.4 Gyr-1, all consistent with the properties of local dwarf galaxies.