Probing Spatial Variations in IGM Transmission: Higher Ly$α$ Visibility in an H$α$-Selected Galaxy Overdensity at $z\simeq6.2$
Year: 2026
Type: preprint
Abstract: The visibility of Ly$α$ emission during the epoch of reionization depends on both galaxy properties and the transmission of Ly$α$ photons through the intergalactic medium (IGM). Using JWST/NIRCam F470N imaging, we identify a prominent projected overdensity of H$α$ emitters (HAEs) at $z\simeq6.2$ in CEERS field. We use Subaru/HSC NB872 imaging to measure their Ly$α$ fluxes and compare the Ly$α$ visibility of galaxies within $2'$ of the density center with that of galaxies outside this region. The Ly$α$-emitter (LAE) fraction is $0.41^{+0.15}_{-0.14}$ in the inner region and $0.27^{+0.19}_{-0.15}$ in the outer region. Stacking the H$α$ and Ly$α$ images gives median Ly$α$ escape fractions of $0.100^{+0.091}_{-0.053}$ and $0.063^{+0.130}_{-0.063}$ in the inner and outer regions, respectively. Both measures indicate higher Ly$α$ visibility in the inner region, although only at modest significance. HAEs closer to the density center are systematically more massive and have redder UV slopes, which instead favor lower Ly$α$ escape. The environmental difference in Ly$α$ visibility is therefore difficult to explain solely by variations in underlying galaxy population. Our results are consistent with reduced Ly$α$ attenuation through a more highly ionized IGM in the overdense region, as expected if large H\,{\sc ii} bubbles preferentially form around such galaxy overdensities. The wide-field LAE distribution provides complementary support for this scenario, as the HAE-defined density center coincides with the strongest LAE overdensity across the $1.4\,{\rm deg}^2$ HSC field. These findings highlight the importance of spatial variations in IGM attenuation in shaping Ly$α$ visibility near the end of reionization.
Source: arXiv (Cornell University)
Institutions: The University of Tokyo, Peking University, Waseda University, Waseda Research Institute for Science and Engineering, DTU Space, Technical University of Denmark, Tohoku University, Kwansei Gakuin University, National Astronomical Observatory of Japan, Institute for Cosmic Ray Research, Kavli Institute for the Physics and Mathematics of the Universe, Waseda Institute for Advanced Study, Hosei University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, National Aeronautics and Space Administration, Gordon and Betty Moore Foundation, Princeton University, Johns Hopkins University, Space Telescope Science Institute, Queen's University Belfast, Durham University, Ministry of Education, Culture, Sports, Science and Technology, Danmarks Grundforskningsfond, Academia Sinica, Cabinet Office, Government of Japan, Max-Planck-Gesellschaft, National Central University, National Astronomical Observatory of Japan, High Energy Accelerator Research Organization, Eötvös Loránd Tudományegyetem, Max-Planck-Institut für Astronomie, Toray Science Foundation, Smithsonian Astrophysical Observatory, Science Mission Directorate, Japan Society for the Promotion of Science, Japan Science and Technology Agency, Planetary Science Division, Los Alamos National Laboratory
Awards: G103270039, Galaxy formation and evolution in cosmic supervoids revealed by Subaru/PFS, G1219399070, G256731684, Comprehensive study of the feedback efficiency of AGN outflows to host galaxies, Towards Ultimate Subaru: Galaxy formation history probed by deep near-infrared imaging with wide-field adaptive optics, G4286721033, G4474636675, Frontiers of Cosmic Reionization and Galaxy Formation Opened Up by the Massive Spectroscopic Survey with Subaru PFS, G5568641063, Probing the origin of supermassive black holes with Subaru Telescope, JWST, and Euclid, G618131832, G6474273050, A NEO SEARCH PROGRAM USING THE PAN-STARRS PS1 TELESCOPETHE GOAL OF THE PROPOSED RESEARCH IS TO USE T, Investigating the Galaxy-Cosmic Web Connection with Subaru PFS, Galaxy Overdense Regions in the Distant Universe Revealed by Wide-Area Sky Survey and TAO, Relationship between Protoclusters and Cosmic Reionization Revealed by the Strongest Tag Team of JWST and ALMA, Baryon Cycle Around Galaxies and Intergalactic Medium Probed with Narrowband Imaging, G7187964967, 狭帯域フィルターでひらく銀河・銀河間物質をめぐる物質循環の新展開, Theoretical and observational research to resolve the bright-end excess problem of ultraviolet luminosity functions of very high redshift galaxies, Pan-STARRS1: Operations; Public Data Release; Education and Outreach, 宇宙最大規模天体の探査と解剖：構造形成論の検証と銀河・ブラックホール形成の解明, G833430883, G9000359136
OpenAlex ID: W7214762679