First Spectroscopic Confirmations of z ∼ 7.0 Lyα Emitting Galaxies in the LAGER Survey

Abstract

Narrowband imaging is a highly successful approach for finding large numbers of high redshift Lyα emitting galaxies (LAEs) up to z ∼ 6.6. However, at z 7 there are as yet only 3 narrowband selected LAEs with spectroscopic confirmations (two at z ∼ 6.9 − 7.0, one at z ∼ 7.3), which hinders extensive studies on cosmic reionization and galaxy evolution at this key epoch. We have selected 23 candidate z ∼ 6.9 LAEs in COSMOS field with the large area narrowband survey LAGER (Lyman-Alpha Galaxies at the End of Reionization). In this work we present spectroscopic followup observations of 12 candidates using IMACS on Magellan. For 9 of these, the observations are sufficiently deep to detect the expected lines. Lyα emission lines are identified in six sources (yielding a success rate of 2/3), including 3 luminous LAEs with Lyα luminosities of L Lyα ∼ 10 43.5 erg s −1 , the highest among known spectroscopically confirmed galaxies at 7.0. This triples the sample size of spectroscopically confirmed narrowband selected LAEs at z 7, and confirms the bright end bump in the Lyα luminosity function we previously derived based on the photometric sample, supporting a patchy reionization scenario. Two luminous LAEs appear physically linked with projected distance of 1.1 pMpc and velocity difference of ∼ 170 km s −1 . They likely sit in a common ionized bubble produced by themselves or with close neighbors, which reduces the IGM attenuation of Lyα. A tentative narrow N vλ1240 line is seen in one source, hinting at activity of a central massive black hole with metal rich line emitting gas.

Lyα Galaxies in the Epoch of Reionization (LAGER): Spectroscopic Confirmation of Two Redshift ∼7.0 Galaxies

“…In the first result, we found 23 z ≈ 7 Lyα emitters and showed that the z ≈ 7 Lyα luminosity function in the COSMOS deep field has an excess of the brightest source . We have confirmed these bright LAEs using spectroscopy from Magellan/IMACS (Hu et al 2017).…”

“…The current estimate of the neutral hydrogen fraction of the IGM is x HI = 0.3±0.2 at z ≈ 6.6 based on Lyα luminosity function (Konno et al 2018). At z 7.0, Lyα searches (Tilvi et al 2010;Konno et al 2014;Zheng et al 2017;Ota et al 2017;Itoh et al 2018) have found a few tens LAEs and shown a significant drop of the Lyα luminosity function relative to the one at z ≈ 6.6.…”

“…The Lyα luminosity function observed at z ≈ 6.6 shows modest evolution from those at z ≈ 5.7 (e.g. Malhotra & Rhoads 2004;Hu et al 2010;Ouchi et al 2010;Kashikawa et al 2011;Konno et al 2018). The current estimate of the neutral hydrogen fraction of the IGM is x HI = 0.3±0.2 at z ≈ 6.6 based on Lyα luminosity function (Konno et al 2018).…”

A Magellan M2FS Spectroscopic Survey of Galaxies at 5.5 < z < 6.8: Program Overview and a Sample of the Brightest Lyα Emitters

“…Three dark atmospheric windows with little OH sky emission in the optical are often used to detect galaxies at z 5.7  , 6.5, and 6.9. More than 200 LAEs have been spectroscopically confirmed at these redshifts (e.g., Taniguchi et al 2005;Iye et al 2006;Kashikawa et al 2006Kashikawa et al , 2011Shimasaku et al 2006;Hu et al 2010;Ouchi et al 2010;Rhoads et al 2012;Zheng et al 2017;Hu et al 2017). The narrowband technique is also being used to search for higherredshift LAEs at z 7 > (e.g., Hibon et al 2010;Tilvi et al 2010;Krug et al 2012;Ota & Iye 2012;Shibuya et al 2012;Konno et al 2014).…”

RELICS: spectroscopy of gravitationally lensed z ≃ 2 reionization-era analogues and implications for C iii] detections at z &gt; 6

“…Strong nebular CIV emission has been detected in two low mass z > 6 galaxies (Stark et al 2015b;Mainali et al 2017;Schmidt et al 2017), pointing to a hard ionizing spectrum that is usually associated with active galactic nuclei (AGNs) in galaxies at lower redshifts (Hainline et al 2011;Le Fèvre et al 2017). Most recently, the nebular NV emission line has been reported in several additional z > 7 galaxies (Hu et al 2017;Tilvi et al 2016;Laporte et al 2017;Mainali et al 2018), requiring an intense radiation field with significant flux of photons more energetic than 77 eV. Many of these sources have IRAC colors that are suggestive of extreme optical line emission (EW [OIII]+Hβ 1000-2000Å), larger than the typical values inferred at z 7.…”