A giant galaxy in the young Universe with a massive ring




Yuan, Tiantian
Elagali, A.
Labbe, Ivo
Kacprzak, Glenn
Lagos , Claudia del P.
Alcorn , Leo Y.
Cohn, Jonathan H.
Tran , Kim-Vy H.
Glazebrook , Karl
Groves, Brent

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Nature Publishing Group


In the local (redshift z≈ 0) Universe, collisional ring galaxies make up only ~0.01% of galaxies1 and are formed by head-on galactic collisions that trigger radially propagating density waves2-4. These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe. However, not much is known about distant (z> 0.1) collisional rings10-14. Here we present a detailed study of a ring galaxy at a look-back time of 10.8 Gyr (z= 2.19). Compared with our Milky Way, this galaxy has a similar stellar mass, but has a stellar half-light radius that is 1.5-2.2 times larger and is forming stars 50 times faster. The extended, diffuse stellar light outside the star-forming ring, combined with a radial velocity on the ring and an intruder galaxy nearby, provides evidence for this galaxy hosting a collisional ring. If the ring is secularly evolved15,16, the implied large bar in a giant disk would be inconsistent with the current understanding of the earliest formation of barred spirals17-21. Contrary to previous predictions10-12, this work suggests that massive collisional rings were as rare 11 Gyr ago as they are today. Our discovery offers a unique pathway for studying density waves in young galaxies, as well as constraining the cosmic evolution of spiral disks and galaxy groups.




Yuan, T., Elagali, A., Labbé, I. et al. A giant galaxy in the young Universe with a massive ring. Nat Astron 4, 957–964 (2020). https://doi.org/10.1038/s41550-020-1102-7


Nature Astronomy


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