ビッグバン後14億年で巨大銀河が形成された可能性を解明 (How giant galaxies could form just 1.4 billion years after the big bang)

2026-02-10 マックス・プランク研究所

Clusters of young galaxies in the early Universe that later grow into large clusters are called protoclusters. This artist’s impression of the protocluster SPT2349-56 shows interacting galaxies of different shapes and sizes, and gas (orange) that is torn apart and heated by tidal forces. Due to its great distance from Earth, we see SPT2349-56 as it looked only 1.4 billion years after the Big Bang, when the Universe was 10% of its current age.© N.Sulzenauer, MPIfR

＜関連情報＞

• https://www.mpg.de/26119786/forming-massive-galaxies-in-the-early-universe
• https://iopscience.iop.org/article/10.3847/1538-4357/ae2ff0

SPT2349-56における巨大銀河形成の指標となる明るい[C II ]158 μmストリーマー（ z = 4.3） Bright [C II]158 μm Streamers as a Beacon for Giant Galaxy Formation in SPT2349-56 at z = 4.3

Nikolaus Sulzenauer, Axel Weiß, Ryley Hill, Scott C. Chapman, Manuel Aravena, Veronica J. Dike, Anthony Gonzalez, Duncan MacIntyre, Desika Narayanan, Kedar A. Phadke,…
The Astrophysical Journal  Published: 2026 February 10
DOI:10.3847/1538-4357/ae2ff0

Abstract

Observations of extreme starbursts, often located in the cores of protoclusters, challenge the classical bottom-up galaxy formation paradigm. Giant elliptical galaxies at z = 0 must have assembled rapidly, possibly within few 100 Myr through an extreme growth phase at high-redshift, characterized by elevated star formation rates of several thousand solar masses per year distributed over concurrent, gas-rich mergers. We present a novel view of the z = 4.3 protocluster core SPT2349–56 from sensitive multicycle Atacama Large Millimeter/submillimeter Array dust continuum and [C ii]158μm line observations. Distributed across 60 kpc, a highly structured gas reservoir with a line luminosity of L_{[C II]} = 3.0 ± 0.2 × 10⁹ L_⊙ and an inferred cold gas mass of M_gas = 8.9 ± 0.7 × 10⁹ M_⊙ is found surrounding the central massive galaxy triplet. Like “beads on a string,” the newly discovered [C ii] streamers fragment into a few kiloparsec-spaced and turbulent clumps that have a similar column density as local Universe spiral galaxy arms at Σ_gas = 20–60 M_⊙ L^-1_⊙pc⁻². For a dust temperature of 30 K, the [C ii] emission from the ejected clumps carries ≳3% of the far-IR luminosity, translating into an exceptionally low mass-to-light ratio of α_[CII] = 2.95 ± 0.3 M_⊙ , indicative of shock-heated molecular gas. In phase space, about half of the galaxies in the protocluster core populate the same caustic as the [C ii] streamers (r/r_vir × ∣Δv∣/σ_vir ≈ 0.1), suggesting angular momentum dissipation via tidal ejection while the brightest cluster galaxy (BCG) is assembling. Our findings provide new evidence for the importance of tidal ejections of [C ii]-bright, shocked material following multiple major mergers that might represent a landmark phase in the z ≳ 4 coevolution of BCGs with their hot, metal enriched atmospheres.