Direct evidence for Ly$\alpha$ depletion in the protocluster core

Abstract

We have carried out a panoramic Ly$\alpha$ narrowband imaging with Suprime-Cam on Subaru towards the known protocluster USS1558--003 at $z=2.53$. Our previous narrowband imaging at near-infrared has identified multiple dense groups of H$\alpha$ emitters (HAEs) within the protocluster. We have now identified the large-scale structures across a $\sim$50 comoving Mpc scale traced by Ly$\alpha$ emitters (LAEs) in which the protocluster traced by the HAEs is embedded. On a smaller scale, however, there are remarkably few LAEs in the regions of HAE overdensities. Moreover, the stacking analyses of the images show that HAEs in higher-density regions show systematically lower escape fractions of Ly$\alpha$ photons than those of HAEs in lower-density regions. These phenomena may be driven by the extra depletion of Ly$\alpha$ emission lines along our line of sight by more intervening cold circumgalactic/intergalactic medium and/or dust existing in the dense core. We also caution that all the past high-$z$ protocluster surveys using LAEs as the tracers would have largely missed galaxies in the very dense cores of the protoclusters where we would expect to see any early environmental effects.

6 pages, 4 figures, accepted for publication in MNRAS Letter

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• The Stellar Mass, Star Formation Rate and Dark Matter Halo Properties of LAEs at $z\sim 2$
• Discovery of Protoclusters at z~3.7 & 4.9: Embedded in Primordial Superclusters
• Lyman-Alpha Escape from Low-Mass, Compact, High-Redshift Galaxies
• The physical origin for spatially large scatter of IGM opacity at the end of reionization: the IGM Ly$\alpha$ opacity-galaxy density relation
• Lyα Halos around [O III]-Selected Galaxies in HETDEX
• Extended star-forming region within galaxies in a dense proto-cluster core at z=2.53
• Stellar Populations of Lyman-alpha Emitting Galaxies in the HETDEX Survey I: An Analysis of LAEs in the GOODS-N Field
• UV & Ly$\alpha$ halos of Ly$\alpha$ emitters across environments at z=2.84
• The environments and hosts of metal absorption at z>5
• Are Lyα emitters segregated in protoclusters regions?