Title: Formation and Environmental Context of Giant Bulgeless Disk Galaxies in the Early Universe: Insights from Cosmological Simulations Show Chinese title

Title: 早期宇宙中无巨核盘星系的形成与环境背景：来自宇宙学模拟的启示

Abstract: Giant bulgeless disk galaxies, theoretically expected to be rare in the early Universe, have been confirmed by the James Webb Space Telescope (JWST) to exist as early as 2 billion years after the Big Bang. These morphologically extreme systems offer valuable insights into the physics of disk formation and the interplay between galaxies and their dark-matter halos. Using cosmological simulations, we identify analogs of such galaxies with stellar masses around $10^{11} M_\odot$ and half-light radii up to 6 kpc at $z \sim 3$ and characterize the factors that contribute to their formation. These galaxies form in young cosmic knots, populating host halos of high spin, low concentration, and spherical shapes. They feature dynamically coherent circum-galactic medium, as well as gas-rich, coherent mergers, which preserve their disk morphology and drive their large sizes. Interestingly, all the simulated giant disks harbor a compact, aligned inner disk, marginally resolvable in JWST images with a S\'ersic index near unity. These findings highlight the environmental and structural conditions necessary for forming and sustaining giant bulgeless disks and provide a theoretical framework for interpreting JWST observations of extreme disk morphologies in the early Universe. Show Chinese abstract

Abstract: 没有巨大 bulge 的巨型盘状星系，在理论上预计在早期宇宙中是罕见的，但通过詹姆斯韦布太空望远镜（JWST）已经确认它们在大爆炸后 20 亿年就存在了。这些形态极端的系统为盘状星系形成物理机制以及星系与其暗物质晕之间的相互作用提供了宝贵的见解。使用宇宙学模拟，我们识别出类似这种星系的模拟对象，其恒星质量约为$10^{11} M_\odot$，在$z \sim 3$时半光半径可达 6 千秒差距，并且研究了促成它们形成的因素。这些星系形成于年轻的宇宙节点中，占据高自旋、低浓度和球形的宿主晕。它们具有动态一致的星系际介质，以及富含气体且一致合并的星系，这保留了它们的盘状形态并促成了它们的大尺寸。有趣的是，所有模拟出的巨型盘状星系都包含一个紧凑且对齐的内盘，在 JWST 图像中用接近 1 的 Sérsic 指数可以部分解析到。这些发现突出了形成和维持巨型无 bulge 盘所需的环境和结构条件，并为解释 JWST 对早期宇宙中极端盘状形态的观测提供了一个理论框架。