Diverse Metallicities in Protoclusters at z ~ 3.4 detected by Deep Learning
Year: 2026
Type: article
Abstract: We present spectroscopic follow-up observations with Subaru/MOIRCS of four protocluster candidate regions identified by the deep-learning model PCFNet. In three candidate regions, we confirm four protoclusters at z = 3.316, 3.403, 3.408 and 3.425, exhibiting galaxy density peaks over five times the uniform distribution. The detection rate of confirmed members aligns with PCFNet’s predictions, underscoring its effectiveness. Analysis of spectral energy distributions (SEDs), incorporating up to ten photometric bands (uu*grizyJHK), reveals that protocluster members lie on the star-formation main sequence. The masses of the most massive halos in the protoclusters are estimated from the most massive stellar mass of the member galaxies, yielding log Mhalo/M⊙ = 12.4–12.8, which are consistent with those at this redshift predicted by cosmological simulations and are comparable to those of the progenitors of typical local clusters ($M_\mathrm{halo}^{z=0}\sim 10^{14}M_\odot$). Using the Voronoi Tessellation Monte Carlo technique based on the probability of protocluster membership from PCFNet, we find that our protoclusters exhibit a significantly higher SFRD than the cosmic SFRD at z ~ 3.4. Based on the [O iii]/Hβ emission line ratio, two protoclusters show marginally (1.4–2σ) higher average metallicities than the field, while the other protoclusters are statistically consistent with the field. These diverse metallicities highlight the environmental impact within protoclusters detected by PCFNet, likely reflecting the complex opposing interplay between metal-rich gas recycling and metal-poor gas inflow, which may depend on the surrounding environment of each protocluster. This work demonstrates PCFNet’s capability to unveil diverse samples of high-redshift protoclusters, paving the way for a more comprehensive understanding of their role in galaxy evolution.
Institutions: The University of Tokyo, Research Center for the Early Universe, DTU Space, Technical University of Denmark, University of Hyogo, Tohoku University, Nishi-Harima Astronomical Observatory, Kwansei Gakuin University, Carnegie Institution for Science, Carnegie Observatories, National Astronomical Observatory of Japan, Institute for Cosmic Ray Research, Hosei University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
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, 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: Galaxy formation and evolution in cosmic supervoids revealed by Subaru/PFS, Comprehensive study of the feedback efficiency of AGN outflows to host galaxies, G4474636675, G618131832, A NEO SEARCH PROGRAM USING THE PAN-STARRS PS1 TELESCOPETHE GOAL OF THE PROPOSED RESEARCH IS TO USE T, Galaxy Overdense Regions in the Distant Universe Revealed by Wide-Area Sky Survey and TAO, G7187964967, Pan-STARRS1: Operations; Public Data Release; Education and Outreach, G833430883
OpenAlex ID: W7214745784