New spectroscopic confirmations of Lyman-$\alpha$ emitters at z $\sim$ 7
  from the LAGER survey
  We report spectroscopic confirmations of 15 Lyman-alpha galaxies at $z\sim7$,
implying a spectroscopic confirmation rate of $\sim$80% on candidates selected
from LAGER (Lyman-Alpha Galaxies in the Epoch of Reionization), which is the
largest (24 deg$^2$) survey aimed at finding Lyman-alpha emitters (LAEs) at
$z\sim7$ using deep narrow-band imaging from DECam at CTIO. LAEs at
high-redshifts are sensitive probes of cosmic reionization and narrow-band
imaging is a robust and effective method for selecting a large number of LAEs.
In this work, we present results from the spectroscopic follow-up of LAE
candidates in two LAGER fields, COSMOS and WIDE-12, using observations from
Keck/LRIS. We report the successful detection of Ly$\alpha$ emission in 15
candidates (11 in COSMOS and 4 in WIDE-12 fields). Three of these in COSMOS
have matching confirmations from a previous LAGER spectroscopic follow-up and
are part of the overdense region, LAGER-$z7$OD1. Additionally, two candidates
that were not detected in the LRIS observations have prior spectroscopic
confirmations from Magellan. Including these, we obtain a spectroscopic
confirmation success rate of $\sim$$80$% for LAGER LAE candidates. Apart from
Ly$\alpha$, we do not detect any other UV nebular lines in our LRIS spectra;
however, we estimate a 2$\sigma$ upper limit for the ratio of NV/Ly$\alpha$,
$f_{NV}/f_{Ly\alpha} \lesssim 0.27$, which implies that ionizing emission from
these sources is mostly dominated by star formation. Including confirmations
from this work, a total of 33 LAE sources from LAGER are now spectroscopically
confirmed. LAGER has more than doubled the sample of spectroscopically
confirmed LAE sources at $z\sim7$.
