Spitzer constraints on the z =6.56 galaxy lensed by Abell 370

We report on Spitzer IRAC observations of the spectroscopically confirmed z = 6.56 lensed Lya emitting source HCM 6A that was found behind the cluster Abell 370. Detection of the source at 3.6 and 4.5 mu m, corresponding to rest-frame optical emission, allows us to study the stellar population of this primeval galaxy. The broadband flux density at 4.5 mm is enhanced compared to the continuum at other wavelengths, likely due to the presence of strong Ha in emission. The derived Ha line flux corresponds to a star formation rate of greater than or similar to 140 M-circle dot yr(-1), more than an order of magnitude larger than estimates from the ultraviolet continuum and Lya emission line. The dust extinction required to explain the discrepancy is A(v) similar to 1 mag. The inference of dust at such high redshifts is surprising and implies that the first epoch of star formation in this galaxy occurred at z similar to 20