2015ApJ...804...11P

We report on our first set of spectroscopic Hubble Space Telescope observations of the z ≈ 11 candidate galaxy, which is strongly lensed by the MACSJ 0647.7+7015 galaxy cluster. The three lensed images are faint and we show that these early slitless grism observations are of sufficient depth to investigate whether this high-redshift candidate, identified by its strong photometric break at ≈1.5 µm, could possibly be an emission line galaxy at a much lower redshift. While such an interloper would imply the existence of a rather peculiar object, we show here that such strong emission lines would clearly have been detected. Comparing realistic, two-dimensional simulations to these new observations, we would expect the necessary emission lines to be detected at > 5 σ, though we see no evidence for such lines in the dispersed data of any of the three lensed images. We therefore exclude that this object could be a low-redshift emission line interloper, which significantly increases the likelihood of this candidate being a bona fide z ≈ 11 galaxy.