* Astronomy

Title: CLASH: Discovery of a Bright z ~ 6.2 Dwarf Galaxy Quadruply Lensed by MACS J0329.6-0211
Authors: A. Zitrin, J. Moustakas, L. Bradley, D. Coe, L.A. Moustakas, M. Postman, X. Shu, W. Zheng, N. Benítez, R. Bouwens, T. Broadhurst, H. Ford, O. Host, S. Jouvel, A. Koekemoer, M. Meneghetti, P. Rosati, C. Grillo, D. Kelson, D. Lemze, E. Medezinski, A. Molino, M. Nonino, S. Ogaz

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 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 z_{s}\simeq2-4. 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\simeq6.2 galaxy occupies a source-plane area of approximately 2.2 kpc^{2}. Modelling the observed spectral energy distribution using population synthesis models, we find a demagnified stellar mass of ~10^{9} \mathcal{M}_{\sun}, subsolar metallicity (Z/Z_{\sun} ~0.5), low dust content (A_{V}~0.1 mag), a demagnified star formation rate (SFR) of ~3.2 \mathcal{M}_{\sun} yr^{-1}, and a specific SFR of ~3.4 Gyr^{-1}, all consistent with the properties of local dwarf galaxies.

Read more (1989kb, PDF)