Speaker
Description
We examine the morphological evolution of galaxies at late cosmic times ($z<4$) using Horizon Run 5 (HR5) cosmological hydrodynamic simulation. Building upon previous analyses, we classify galaxies with stellar mass $M_∗>2×10^9 M_{\odot}$ into disk, spheroid, and irregular types based on non-parametric structural diagnostics, primarily asymmetry and Sérsic index. At $z\sim0.625$, we find that ~80% of galaxies exhibit a Sérsic index less than 1.5, indicative of disk-dominated morphologies. This fraction declines with increasing redshift and stellar mass. In contrast, kinematic classification using the ratio of rotational velocity to stellar velocity dispersion (v/$\sigma$) reveals a predominance of slow rotators (with v/$\sigma>0.55$) in the low-mass regime at the same epoch. Considering the dominance of disk-like morphology based on structural classification, we would expect to see a corresponding dominance of fast rotators (v/$\sigma>0.55$) in the similar mass range. We explore the role of merger history and stellar mass assembly in driving this structural–kinematic discrepancy. Given the remarkable agreement of HR5 results with JWST observations at high redshift, resolving this structural–kinematic discrepancy at low redshift will offer deeper insights into both the galaxy evolutionary process and the predictive power of the simulations.
