Misc,
Keck/MOSFIRE Spectroscopy of z=7-8 Galaxies: Lyman-alpha Emission from a Galaxy at z=7.66
(2016)cite arxiv:1602.02160Comment: 9 pages, 4 figures, submitted to the ApJ.
Abstract
We report the results from some of the deepest Keck/MOSFIRE data yet obtained
for candidate $z 7$ galaxies. Our data show one significant line
detection with 6.5$\sigma$ significance in our combined 10 hours of integration
which is independently detected on more than one night, ruling out the
possibility that the detection is spurious. The asymmetric line profile and
non-detection in the optical bands strongly imply that the detected line is
Ly$\alpha$ emission from a galaxy at $z$(Ly$\alpha)=7.6637 0.0011$, making
it the fourth spectroscopically confirmed galaxy at $z>7.5$. This galaxy is
bright in the rest-frame ultraviolet (UV; $M_UV -21.2$) with a
moderately blue UV slope ($\beta=-2.2^+0.3_-0.2$), and exhibits a
rest-frame Ly$\alpha$ equivalent width of EW(Ly$\alpha$) $\sim
15.6^+5.6_-3.6$ \AA. The non-detection of the 11 other $z \sim$ 7--8
galaxies in our long 10 hr integration, reaching a median 5$\sigma$ sensitivity
of 28 \AA\ in the rest-frame EW(Ly$\alpha$), implies a 1.3$\sigma$ deviation
from the null hypothesis of a non-evolving distribution in the rest-frame
EW(Ly$\alpha$) between $3<z<6$ and $z=$ 7--8. Our results are consistent with
previous studies finding a decline in Ly$\alpha$ emission at $z>6.5$, which may
signal the evolving neutral fraction in the intergalactic medium at the end of
the reionization epoch, although our weak evidence suggests the need for a
larger statistical sample to allow for a more robust conclusion.
