Abstract

We spectroscopically confirmed two narrowband-selected redshift 7.0 Ly alpha galaxies and studied their rest-frame UV spectra. The Ly alpha and other UV nebular lines are very useful to confirm the galactic redshifts and diagnose the different mechanisms driving the ionizing emission. We observed two narrowband-selected z = 7.0 Ly alpha candidates in the LAGER Chandra Deep Field South (CDFS) field with IMACS at the Magellan telescope and confirmed they are Ly alpha emitters at z = 6.924 and 6.931. In one galaxy, we also obtained deep near-infrared (NIR) spectroscopy, which yields non-detections of the high-ionization UV nebular lines. We measured the upper limits of the ratios of C IV lambda 1548/Ly alpha, He II lambda 1640/Ly alpha, O III]lambda 1660/Ly alpha, and C III]lambda 1909/Ly alpha from the NIR spectra. These upper limits imply that the ionizing emission in this galaxy is dominated by normal star formation instead of an active galactic nucleus.