Kavli Affiliate: Yingjie Peng
| First 5 Authors: Fangzhou Jiang, Jinning Liang, Bingcheng Jin, Zeyu Gao, Weichen Wang
| Summary:
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.
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