Ja En つくば宇宙フォーラム
第163回
Thin and thick disk formation from JWST and ALMA observations
津久井 崇史 氏
東京大学 カブリ数物連携宇宙研究機構
要旨
Present-day disk galaxies exhibit a two-layered structure, a thick disk and a thin disk. However, their structural growth history and dynamical properties across cosmic time remain to be understood. Leveraging JWST’s superb capability, we identify thin and thick stellar disks in galaxies up to 10 Gyr ago and measure their structural properties separately. These measurements reveal a sequential picture in which the thick disk forms first, followed by the thin disk formation. Moreover, thin disk formation occurs earlier in high-mass galaxies (~8 Gyr ago) and later in low-mass galaxies (~4 Gyr ago), consistent with the Milky Way's mass evolution track and the estimated age of the oldest thin disk. We also found that the thick disks form geometrically thin and then rapidly become thick. The structural evolution is likely driven by internal processes, as we see no significant disk flaring, which would be expected if external processes dominated (e.g. mearger), and the strong mass-size-thickness relation suggests that it is set by the galaxy properties such as disk mass or surface density. I will present how varying gas fractions may play a major role in driving early thick-disk formation (the rapid thickening phase) and later thin-disk growth, supported by numerical simulations and ALMA observations. I will discuss the Milky Way in the broader context of galaxy formation, with the insights from extragalactic observations.