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arXiv · 1804.00041

Spectroscopic Constraints on UV Metal Line Emission at z~6-9: The Nature of Lyman-alpha Emitting Galaxies in the Reionization-Era

Ramesh Mainali·Adi Zitrin·Daniel P. Stark·Richard S. Ellis·Johan Richard·Mengtao Tang·Nicolas Laporte·Pascal Oesch·Ian McGreer
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Abstract

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 5.4 7 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 (FWHM<90 km/s) and is likely nebular in origin. A deep H-band spectrum of EGSY8p7 reveals non-detections of CIV, He II, and OIII]. The presence of NV requires a substantial flux of photons above 77 eV, pointing to a hard ionizing spectrum powered by an AGN or fast radiative shocks. Regardless of its origin, the intense radiation field of EGSY8p7 may aid the transmission of Lyman-alpha through what is likely a partially neutral IGM. With this new detection, five of thirteen known Lyman-alpha emitters at z>7 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.

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Ramesh Mainali, Adi Zitrin, Daniel P. Stark, Richard S. Ellis, Johan Richard, Mengtao Tang, Nicolas Laporte, Pascal Oesch, Ian McGreer. 2018-03-30. Spectroscopic Constraints on UV Metal Line Emission at z~6-9: The Nature of Lyman-alpha Emitting Galaxies in the Reionization-Era. https://doi.org/10.1093/mnras%2Fsty1640

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