H i absorbers as beacons of hidden structure at z ∼ 3: multicomponent, metal-rich absorption system near a protocluster
Year: 2026
Type: article
Abstract: ABSTRACT H i gas traces the large-scale structure and provides the primary fuel for star formation. High-z protoclusters are ideal laboratories to study how H i gas is accreted and consumed during the formation of the most massive structures in the Universe. However, much remains unknown about the distribution and physical state of their H i gas. We examine a rare configuration in which a protocluster candidate is located in front of a quasar at $z=3.09$. Our spectroscopic campaign confirms a protocluster at $z = 3.079$; however, no corresponding strong H i absorption is found in the background quasar spectrum. Instead, we serendipitously discover a prominent H i absorption feature at $z\sim 3.01$, offset by $\sim 60$ cMpc from the centre of the protocluster. Spanning an exceptionally broad velocity range of $\sim 2000\, \mathrm{km\, s^{-1}}$ ($\sim 40\, \mathrm{cMpc}$), this absorption is decoupled from the confirmed member galaxies. Detailed kinematic modelling reveals this absorption comprises five distinct components rather than a single cloud. Moreover, one of these components exhibits a super-solar metallicity $(\mathrm{[O/H]} = +1.19^{+0.91}_{-0.78})$. We propose two physical scenarios for this unique system: (1) an additional, hidden massive protocluster along the line of sight, and/or (2) metal-rich outflows and metal-poor inflows driven by a single massive galaxy. The discovery highlights that while protoclusters are not universally associated with strong H i absorption, targeting the strong H i absorbers may serve as a beacon for uncovering massive, metal-rich protoclusters or complex gas kinematics in the early Universe.
Institutions: The University of Tokyo, Shinshu University, Tohoku University, Hosei University, National Astronomical Observatory of Japan, DTU Space, Technical University of Denmark, Nara Prefectural University, Kwansei Gakuin University, Institute for Cosmic Ray Research, Saint Mary's University, Waseda University, Waseda Institute for Advanced Study
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, Smithsonian Institution, National Aeronautics and Space Administration, Princeton University, Johns Hopkins University, Canadian Foundation for AIDS Research, Compute Canada, Space Telescope Science Institute, Japan Society for the Promotion of Science London, Queen's University Belfast, Durham University, National Research Foundation, Ministry of Education, Culture, Sports, Science and Technology, Danmarks Grundforskningsfond, Academia Sinica, Chinese Academy of Sciences, Cabinet Office, Government of Japan, Queen's University, Centre National de la Recherche Scientifique, Danmarks Frie Forskningsfond, 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, National Astronomical Observatories, Chinese Academy of Sciences, 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, G7915655429, G833430883, G9000359136
OpenAlex ID: W7204621777