Not In Our Backyard: Spectroscopic Support for the CLASH z=11 Candidate MACS0647-JD

TL;DR

This study uses spectroscopic observations from the Hubble Space Telescope to confirm that a candidate galaxy at redshift ~11 is unlikely to be a lower-redshift interloper, supporting its classification as a genuine high-redshift galaxy.

Contribution

First spectroscopic analysis of the z~11 galaxy candidate, providing evidence against it being a low-redshift interloper and strengthening its high-redshift identification.

Findings

No strong emission lines detected in the spectra.

Excludes low-redshift interloper scenario with >5 sigma confidence.

Supports the candidate being a genuine z~11 galaxy.

Abstract

We report on our first set of spectroscopic Hubble Space Telescope observations of the z~11 candidate galaxy strongly lensed by the MACSJ0647.7+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 micron, 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 sigma while 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.