PAPER / ARXIV:2609.04349
Kentaro Koretomo (1), Nobunari Kashikawa (1 and 2), Toru Misawa (3), Jun Toshikawa (4), Yoshihiro Takeda (1), Hisakazu Uchiyama (5 and 6), Junya Arita (1), Shunta Shimizu (1), Ryo Emori (1), Kei Ito (7 and 8), Satoshi Kikuta (9), Mariko Kubo (4 and 10), Yoshiaki Ono (11), Marcin Sawicki (12), Rhythm Shimakawa (13) ((1) The University of Tokyo, Tokyo, Japan, (2) Center for the Early Universe, The University of Tokyo, Tokyo, Japan, (3) Shinshu University, Matsumoto, Japan, (4) Tohoku University, Sendai, Japan, (5) Hosei University, Tokyo, Japan, (6) National Astronomical Observatory of Japan, Mitaka, Japan, (7) Cosmic Dawn Center, Copenhagen, Denmark, (8) Technical University of Denmark, Lyngby, Denmark, (9) Nara Prefectural University, Nara, Japan, (10) Kwansei Gakuin University, Sanda, Japan, (11) Institute for Cosmic Ray Research, The University of Tokyo, Kashiwa, Japan, (12) Saint Mary's University, Halifax, Canada, (13) Waseda University, Tokyo, Japan)
RESUMO
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 $\sim 2000$ km s$^{-1}$ ($\sim 40$ 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.
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