Ly alpha EMITTER GALAXIES AT z similar to 2.8 IN THE EXTENDED CHANDRA DEEP FIELD SOUTH. I. TRACING THE LARGE-SCALE STRUCTURE VIA Ly alpha IMAGING
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Date
2016
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Publisher
IOP PUBLISHING LTD
Abstract
We present a narrowband survey with three adjacent filters for z - 2.8-2.9 Lyman alpha (Ly alpha) emitter (LAE) galaxies in the Extended Chandra Deep Field South (ECDFS), along with spectroscopic follow-up. With a complete sample of 96 LAE candidates in the narrowband NB466, we confirm the large-scale structure at z similar to 2.8 suggested by 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 similar to 6.0 +/- 0.8 times the standard deviation expected at z similar to 2.8, assuming a linear bias of 2. The overdense large-scale structure in NB466 can be decomposed into four 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 four protoclusters are expected to evolve into a Coma-like cluster (M >= 10(15) M-circle dot) at z similar to 0. We also 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 the Lya, rest-frame UV, and X-ray bands are similar to 4, 10, and < 16 M-circle dot yr(-1), respectively, implying a Ly alpha escape fraction of 25% less than or similar to f(ESC)(Ly alpha) less than or similar to 40% and a UV continuum escape fraction of f(ESC)(UV,cont) greater than or similar to 62% for LAEs at z similar to 2.8. The Ly alpha photon density calculated from the integrated Ly alpha luminosity function in the overdense field (NB466) is similar to 50% higher than that in the blank field (NB470+NB475), and more bright LAEs are found in the overdense field. The three brightest LAEs, including a quasar at z = 2.81, are all detected in the X-ray band and in NB466. These three LAE-active galactic nuclei contribute an extra 20%-30% Lya photon density compared to other LAE galaxies. Furthermore, we find that LAEs in overdense regions have larger equivalent width values, bluer U-B and V-R (similar to 2-3 sigma) 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 similar to 2.8 in the ECDFS field is a very significant and rare density peak similar to the SSA22 protocluster, and narrowband imaging is an efficient method of detecting and studying such structures in the high-z universe.
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Keywords
galaxies: evolution, galaxies: high-redshift, galaxies: luminosity function, galaxies: structure, mass function, LYMAN-BREAK GALAXIES, EMISSION-LINE GALAXIES, STAR-FORMATION RATE, LUMINOSITY FUNCTIONS, RADIO GALAXY, EQUIVALENT WIDTH, SPIDERWEB GALAXY, ESCAPE FRACTION, PROTO-CLUSTER, AGN ACTIVITY