Spectroscopic constraints on UV metal line emission at z ≃ 6-9: the nature of Lyα emitting galaxies in the reionization era

Recent studies have revealed intense UV metal emission lines in a modest sample of z>7 Lyman-alpha emitters, indicating a hard ionizing spectrum is present. If such high ionization features are shown to be common, it may indicate that extreme radiation fields play a role in regulating the visibility of Lyman-alpha in the reionization era. Here we present deep near-infrared spectra of seven galaxies with Lyman-alpha emission at 5.47 photometric targets. In nine sources we do not detect UV metal lines. However in the z=8.683 galaxy EGSY8p7, we detect a 4.6 sigma emission line in the narrow spectral window expected for NV 1243. The feature is unresolved (FWHM7 have now been shown to have intense UV line emission, suggesting that extreme radiation fields are commonplace among the Lyman-alpha population. Future observations with JWST will eventually clarify the origin of these features and explain their role in the visibility of Lyman-alpha in the reionization era.
Comment: 15 pages, 3 tables and 7 figures. Accepted for publication in MNRAS