First Spectroscopic Confirmations of z similar to 7.0 Ly alpha Emitting Galaxies in the LAGER Survey

摘要

Narrowband imaging is a highly successful approach for finding large numbers of high-redshift Ly alpha emitting galaxies (LAEs) up to z similar to 6.6. However, at z greater than or similar to 7 there are as of yet only three narrowband selected LAEs with spectroscopic confirmations (two at z similar to 6.9-7.0, one at z similar to 7.3), which hinders extensive studies on cosmic reionization and galaxy evolution at this key epoch. We have selected 23 candidate z similar to 6.9 LAEs in COSMOS field with the large area narrowband survey Lyman-Alpha Galaxies at the End of Reionization (LAGER). In this work, we present spectroscopic follow-up observations of 12 candidates using the Inamori Magellan Areal Camera and Spectrograph on Magellan. For nine of these, the observations are sufficiently deep to detect the expected lines. Ly alpha emission lines are identified in six sources (yielding a success rate of 2/3), including three luminous LAEs with Ly alpha luminosities of L-Ly alpha similar to 10(43.5) erg s(-1), the highest among known spectroscopically confirmed galaxies at greater than or similar to 7.0. This triples the sample size of spectroscopically confirmed narrowband selected LAEs at z greater than or similar to 7, and confirms the bright-end bump in the Ly alpha luminosity function we previously derived based on the photometric sample, supporting a patchy reionization scenario. Two luminous LAEs appear physically linked with a projected distance of 1.1 pMpc and velocity difference of similar to 170 km s(-1). They likely sit in a common ionized bubble produced by themselves or with close neighbors, which reduces the intergalactic medium attenuation of Ly alpha. A tentative narrow N V lambda 1240 line is seen in one source, hinting at activity of a central massive black hole with metal-rich line-emitting gas.