Emergence of Galactic Morphologies at Cosmic Dawn: Input from Numerical Modeling

Abstract

We employ a series of high-resolution zoom-in cosmological simulations to analyze the emerging morphology of main galaxies in dark matter halos at redshifts 𝑧 > ∼ 2. We choose DM halos of similar masses of log 𝑀 vir /M ∼ 11.65 ± 0.05 at the target redshifts of 𝑧 f = 6, 4 and 2. The rationale for this choice, among others, allows us to analyze how the different growth rate in these DM halos propagates down to galaxy scales and affects their basic parameters. Halos were embedded in high or low overdensity regions, and two different versions of a galactic wind feedback have been employed -a strong one and energetically weak one. Our main results are: (1) Although our galaxies evolve in different epochs, their global parameters (e.g., baryonic masses and sizes) remain within a narrow range. Their morphology, kinematics and stellar populations differ substantially, yet all of them host sub-kpc stellar bars; (2) The star formation rates (SFRs) appear higher for larger 𝑧 f , in tandem with their energy and momentum feedback; (3) The stellar kinematics allowed separation of bulge from the stellar spheroid. The existence of disk-like bulges has been revealed based on stellar surface density and photometry, but displayed a mixed disk-like and classical bulges based on their kinematics. The bulge-to-total mass ratios appear independent of the last merger time for all 𝑧 f . The stellar spheroid-to-total mass ratios of these galaxies lie in the range of ∼ 0.5 − 0.8; (4) The synthetic redshifted, pixelized and PSF-degraded JWST images allow to detect stellar disks at all 𝑧 f . Some bars disappear in degraded images, but others remain visible; (5) Based on the kinematic decomposition, for stellar disks separated from bulges and spheroids. we observe that rotational support in disks depends on the feedback type, but increases with decreasing 𝑧 f ; (6) Finally, the ALMA images detect disks at all 𝑧 f , but their spiral structure is only detectable in 𝑧 f = 2 galaxies. We also find that the galaxies follow the Tully-Fisher relation most of their evolution, being separated only by the galactic wind feedback.