Lyα EMITTER GALAXIES AT z ∼ 2.8 IN THE EXTENDED CHANDRA DEEP FIELD SOUTH. I. TRACING THE LARGE-SCALE STRUCTURE VIA Lyα IMAGING^∗

Abstract

We present a narrowband survey with three adjacent filters for z = 2.8-2.9 Lyman Alpha Emitter (LAE) galaxies in the Extended Chandra Deep Field South (ECDFS), along with spectroscopic followup. With a complete sample of 96 LAE candidates in the narrowband NB466, we confirm a large-scale structure at z ∼ 2.8 hinted from previous spectroscopic surveys. Compared to the blank field detected with the other two narrowband filters NB470 and NB475, the LAE density excess in NB466 (900 arcmin 2 ) is ∼ 6.0 ± 0.8 times the standard deviation expected at z ∼ 2.8, assuming a linear bias of 2. The overdense large scale structure in NB466 can be decomposed into 4 protoclusters, whose overdensities (each within an equivalent comoving volume 15 3 Mpc 3 ) relative to the blank field (NB470+NB475) are in the range of 4.6 -6.6. These 4 protoclusters are expected to evolve into a Coma-like cluster (M ≥ 10 15 M ⊙ ) at z ∼ 0. In the meanwhile, we investigate the various properties of LAEs at z = 2.8-2.9 and their dependence on the environment. The average star-formation rates derived from Lyα, rest-frame UV and X-ray are ∼4, 10, and <16 M ⊙ /yr, respectively, implying a Lyα escape fraction of 25% fLyα ESC 40% and a UV continuum escape fraction of f UV,cont ESC62% for LAEs at z ∼ 2.8. The Lyα photon density calculated from the integrated Lyα luminosity function in the overdense field (NB466) is ∼50% higher than that in the blank field (NB470+NB475), and more bright LAEs are found in the overdense field. The 3 brightest LAEs, including a quasar at z =2.81, are all detected in X-ray and in NB466. These three LAE-AGNs contribute an extra 20-30% Lyα photon density compared with that from other LAE galaxies. Furthermore, we find that LAEs in overdense regions have larger EW values, bluer U -B and V -R (∼ 2-3σ) colors compared with those in lower density regions, indicating that LAEs in overdense regions are younger and possible less dusty. We conclude that the structure at z ∼ 2.8 in the ECDFS field is a very significant and rare density peak similar to the SSA 22 protocluster, and narrowband imaging is an efficient method of detecting and studying such structures in the high-z universe.

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

“…Many LAEs from z ∼ 2 to ∼ 6.6 have been selected via narrowband imaging and spectroscopically identified (e.g. Hu & McMahon 1996;Hu et al 2004Hu et al , 2010Wang et al 2009;Rhoads et al 2003Rhoads et al , 2004Dawson et al 2004Dawson et al , 2007Ouchi et al 2005Ouchi et al , 2008Ouchi et al , 2010Tapken et al 2006;Westra et al 2006;Shibuya et al 2014Shibuya et al , 2017Zheng et al 2016).…”

Lyα Profile, Dust, and Prediction of Lyα Escape Fraction in Green Pea Galaxies

“…However, as the current sample covers a large range of f (Cowie et al 2011;Finkelstein et al 2009;Scarlata et al 2009). The magenta dashed line shows the z = 2.8 LAE sample from Zheng et al (2016). The red dotted line shows the z = 5.7 and 6.5 LAE sample from Kashikawa et al (2011). relations between EW(Lyα) and V(red-peak) in high redshift LAEs and LBGs, where the LAEs have high EW(Lyα) and small V(red-peak), while the LBGs have small EW(Lyα) and large V(red-peak) (Shapley et al 2003;Hashimoto et al 2013;Erb et al 2014).…”

“…We compared the EW(Lyα) distribution of these 28 Green Peas to high redshift LAEs samples. The high redshift LAEs samples include a sample of z = 2.8 narrow-band selected LAEs (Zheng et al 2016) and a sample of spectroscopically confirmed LAEs at z=5.7 or 6.5 (Kashikawa et al 2011). To be consistent with the methods used in high-z LAEs studies, we use the EW(Lyα) of Green Peas without correction of the stellar Lyα absorption.…”

“…Thousands of high redshift Lyα emission line galaxies (LAE) have been found in the last two decades (e.g. Dey et al 1998;Hu et al 1998;Rhoads et al 2000;Ouchi et al 2003;Gawiser et al 2006;Wang et al 2009;Kashikawa et al 2011;Erb et al 2014;Matthee et al 2014;Zheng et al 2016). These high redshift LAEs generally have small size, low stellar mass, low dust extinction, low metallicity, young age, and high specific star formation rate (sSFR) (e.g.…”

Lyα and UV Sizes of Green Pea Galaxies

“…Dey et al 1998;Hu et al 1998;Rhoads et al 2000;Ouchi et al 2003;Matthee et al 2014;Zheng et al 2016). At z > 6, the Lyα luminosity, Lyα equivalent width (EW), and spatial clustering of Lyα emitting galaxies (LAEs) are important probes of the reionization of Universe (e.g.…”