Morphology of Galaxies in JWST Fields: Initial Distribution and Evolution of Galaxy Morphology

A recent study from the Horizon Run (HR5) cosmological simulation has predicted that galaxies with log M_∗/M_⊙≲ 10 in the cosmic morning (10≳ z≳ 4) dominantly have disk-like morphology in the ΛCDM universe, which is driven by the tidal torque in the initial matter fluctuations. For a direct comparison with observation, we identify a total of about 19,000 James Webb Space Telescope (JWST) galaxies with log M_∗/M_⊙>9 at z=0.6-8.0 utilizing deep JWST/NIRCam images of publicly released fields, including NEP-TDF, NGDEEP, CEERS, COSMOS, UDS, and SMACS J0723-7327. We estimate their stellar masses and photometric redshifts with the redshift dispersion of σ_ NMAD=0.009 and outlier fraction of only about 6%. We classify galaxies into three morphological types, `disks', `spheroids', and `irregulars', applying the same criteria used in the HR5 study. The morphological distribution of the JWST galaxies shows that disk galaxies account for 60-70% at all redshift ranges. However, in the high-mass regime (log M_∗/M_⊙≳11), spheroidal morphology becomes the dominant type. This implies that mass growth of galaxies is accompanied with morphological transition from disks to spheroids. The fraction of irregulars is about 20% or less at all mass and redshifts. All the trends in the morphology distribution are consistently found in the six JWST fields. These results are in close agreement with the results from the HR5 simulation, particularly confirming the prevalence of disk galaxies at small masses in the cosmic morning and noon.