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 waves^2,3,4. These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe^5,6,7,8,9. However, not much is known about distant (z > 0.1) collisional rings^{10,11,12,13,14}. 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 evolved^15,16, the implied large bar in a giant disk would be inconsistent with the current understanding of the earliest formation of barred spirals^{17,18,19,20,21}. Contrary to previous predictions^10,11,12, 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.

在本地（红移Ž  ≈0）宇宙，碰撞环星系只占〜0.01％的星系¹和由迎面碰撞星系该触发径向传播的疏密波形成^2,3,4。这些打击系统为解剖银河盘提供了重要的快照，并且在当地的宇宙^5,6,7,8,9中进行了广泛的研究。但是，关于远的（z  > 0.1）碰撞环^{10,11,12,13,14知之甚少}。在这里，我们对回溯时间为10.8 Gyr（z = 2.19）。与我们的银河系相比，该星系具有类似的恒星质量，但恒星的半光半径大1.5-2.2倍，形成恒星的速度快50倍。恒星形成环外的散布恒星光，加上恒星环上的径向速度和附近的入侵星系，为该星系提供了一个碰撞环提供了证据。如果环是长期演化的^15,16，则暗示着巨大圆盘中的大棒与当前对最早形成禁止螺旋^{17,18,19,20,21的}理解是不一致的。与先前的预测相反^10,11,12，这项工作表明，大型碰撞环在吉尔11年前和今天一样罕见。我们的发现为研究年轻星系中的密度波，以及限制旋盘和星系组的宇宙演化提供了独特的途径。