Abstract
The James Webb Space Telescope (JWST) has discovered a surprising abundance
of bright galaxy candidates in the very early Universe (<500Myrs after the Big
Bang), calling into question current galaxy formation models. Spectroscopy is
needed to confirm the primeval nature of these candidates, as well as to
understand how the first galaxies form stars and grow. Here we present deep
spectroscopic and continuum ALMA observations towards GHZ2/GLASS-z13, one of
the brightest and most robust candidates at z>10, identified in the GLASS-JWST
Early Release Science Program. While the lack of dust continuum detection
supports its high-redshift nature by ruling out lower redshift dusty
interlopers, we do not detect any bright emission line at the position of the
target despite covering a total of 30GHz and 98% of the source's redshift
probability distribution (z=11.9-13.5). A tentative emission line is identified
0.5arcsec away from the JWST position of GHZ2/GLASS-z13, which would imply a
spectroscopic redshift of z=12.117+/-0.012 if associated with the OIII88um
line. Further confirmation is though necessary to confirm the signal is
astrophysical and associated with the target. The current constraints on the
oxygen line luminosity place it along (or below) the OIII-SFR relation for
metal-poor galaxies. The low metallicity and dust content implied by these
observations are also consistent with the blue UV slope observed by JWST, which
suggest negligible dust attenuation in galaxies at this early epoch. This work
illustrates the synergy between JWST and ALMA and paves the way for future
spectroscopic surveys of z > 10 galaxy candidates.
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