遠方銀河の塊状構造の起源

JWST has also revealed clumpy morphologies in \(z > 6\) galaxies with a high spatial resolution of ~ 100 pc scale without lensing effects (e.g., Hainline+24, Chen+23, Tacchella+23). The formation of clumpy galaxies at lower redshift (z \(\lesssim\) 4) has been studied extensively, both observationally (e.g., Elmegreen+13, Tasca+14, Ribeiro+17) and theoretically (e.g., Ceverino+10, Mandelker+14, 16). Violent disk instability driven by cold gas accretion has been proposed as a key mechanism in these studies. However, the formation of clumpy galaxies at z > 6 remains less understood. In order to investigate the properties of (sub-)galactic clumps around the epoch of reionization (z \(\geq\) 6), I develop clump identification algorithms based on the detectability in recent observations and identify clumps in over 1800 snapshots in FirstLight simulations. Nakazato+24 find that about one-tenth of samples are observable clumpy galaxies at z = 6 - 9, and most clumps are formed through major mergers. The merger-induced clumps are short-lived, and merge within a dynamical time of several tens million years (Figure 4). This formation scenario can explain the star formation history of observed high-redshift galaxies consisting of multiple clumps (e.g. Bradˇac+23, Sugahara+24).

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