We report the discovery of a unique z = 6.027 galaxy , multiply imaged by the cluster Abell 383 and detected in new Hubble Space Telescope ACS and WFC3 imaging , as well as in Warm Spitzer observations .
This galaxy was selected as a pair of i -dropouts ; its suspected high redshift was confirmed by the measurement of a strong Lyman- \alpha line in both images using Keck/DEIMOS .
Combining Hubble and Spitzer photometry after correcting for contamination by line emission ( estimated to be a small effect ) , we identify a strong Balmer break of 1.5 magnitudes .
Taking into account the magnification factor of 11.4 \pm 1.9 ( 2.65 \pm 0.17 mag ) for the brightest image , the unlensed AB magnitude for the source is 27.2 \pm 0.05 in the H band , corresponding to a 0.4 L ^ { * } galaxy , and 25.7 \pm 0.08 at 3.6 \mu m. The UV slope is consistent with \beta \sim 2.0 , and from the rest-frame UV continuum we measure a current star formation rate of 2.4 \pm 1.1 M _ { \odot } /yr .
The unlensed half-light radius is measured to be 300 pc , from which we deduce a star-forming surface density of \sim 10 M _ { \odot } yr ^ { -1 } kpc ^ { -2 } .
The Lyman- \alpha emission is found to be extended over \sim 3″along the slit , corresponding to \sim 5 kpc in the source plane .
This can be explained by the presence of a much larger envelope of neutral hydrogen around the star-forming region .
Finally , fitting the spectral energy distribution using 7 photometric data points with simple SED models , we derive the following properties : very little reddening , an inferred stellar mass of M ^ { * } =6 10 ^ { 9 } M _ { \odot } , and an inferred age of \sim 800 Myrs ( corresponding to a redshift of formation of \sim 18 ) .
The star-formation rate of this object was likely much stronger in the past than at the time of observation , suggesting that we may be missing a fraction of galaxies at z \sim 6 which have already faded in rest-frame UV wavelengths .