New Spectroscopic Confirmations of Lyα Emitters at Z ∼ 7 from the LAGER Survey

Abstract

We report spectroscopic confirmations of 15 Ly α galaxies at z ∼ 7, implying a spectroscopic confirmation rate of ∼80% on candidates selected from the Ly α Galaxies in the Epoch of Reionization (LAGER), which is the largest (24 deg 2 ) survey aimed at finding Ly α emitters (LAEs) at z ∼ 7 and uses deep narrowband imaging from the Dark Energy Camera at CTIO. LAEs at high redshifts are sensitive probes of cosmic reionization, and narrowband 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 α emission in 15 candidates. Three of these in COSMOS have matching confirmations from a previous spectroscopic follow-up and are part of the overdense region, LAGER- z 7OD1. Two other candidates that were not detected with LRIS have prior spectroscopic confirmations from Magellan. Including these, we obtain a spectroscopic confirmation success rate of ∼80% for LAGER LAE candidates. Thorough checks were performed to reject the possibility of these detections being foreground emission resulting with a probability of, at most, one contaminant. We do not detect any other UV nebular lines in our LRIS spectra, apart from Ly α . We estimate a 2 σ upper limit for the ratio of N v /Ly α , f NV / f Ly α ≲ 0.27. 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 ∼ 7.