巨大銀河の発見(Astronomers Find Giant Dinosaur of a Galaxy)

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2025-03-26 カリフォルニア工科大学 (Caltech)

カリフォルニア工科大学(Caltech)の天文学者チームは、これまでに発見された中で最も巨大な銀河の一つを発見しました。この渦巻銀河は、私たちの天の川銀河の約5倍の質量を持ち、面積は2倍に及びます。驚くべきことに、この銀河は宇宙が誕生してからわずか20億年後の初期宇宙に存在していました。研究チームは、この銀河を「ビッグ・ホイール」と名付けました。この発見は、初期宇宙における銀河形成の理解を深める重要な成果とされています。

<関連情報>

ビッグバンから20億年後の巨大円盤銀河 A giant disk galaxy two billion years after the Big Bang

Weichen Wang,Sebastiano Cantalupo,Antonio Pensabene,Marta Galbiati,Andrea Travascio,Charles C. Steidel,Michael V. Maseda,Gabriele Pezzulli,Stephanie de Beer,Matteo Fossati,Michele Fumagalli,Sofia G. Gallego,Titouan Lazeyras,Ruari Mackenzie,Jorryt Matthee,Themiya Nanayakkara &Giada Quadri
Nature Astronomy  Published:17 March 2025
DOI:https://doi.org/10.1038/s41550-025-02500-2

巨大銀河の発見(Astronomers Find Giant Dinosaur of a Galaxy)

Abstract

Observational studies have shown that galaxy disks were already in place in the first few billion years of the Universe. The early disks detected so far, with typical half-light radii of 3 kpc at stellar masses around 1011M for redshift z ≈ 3, are significantly smaller than today’s disks with similar masses, which is in agreement with expectations from current galaxy models. Here we report observations of a giant disk at z = 3.25, when the Universe was only two billion years old, with a half-light radius of 9.6 kpc and stellar mass of 3.7+2.6−2.2×1011M. This galaxy is larger than any other kinematically confirmed disks at similar epochs and is surprisingly similar to today’s largest disks with regard to size and mass. James Webb Space Telescope imaging and spectroscopy reveal its spiral morphology and a rotational velocity consistent with a local Tully–Fisher relationship. Multiwavelength observations show that it lies in an exceptionally dense environment, where the galaxy number density is more than ten times higher than the cosmic average and mergers are frequent. The discovery of such a giant disk suggests the presence of favourable physical conditions for large-disk formation in dense environments in the early Universe, which may include efficient accretion of gas carrying coherent angular momentum and non-destructive mergers between exceptionally gas-rich progenitor galaxies.

1701物理及び化学
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