Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation


Arts and Sciences


Physics and Astronomy

First Advisor

Dr. Isaac Shlosman


Galactic morphology in the contemporary universe results from the convergence of a long list of physical processes, not all of them yet fully understood and quantified. The universe exhibits a hierarchical structure: galaxies grow being immersed in dark matter (DM) halos, which in turn are fed by diffuse and filamentary accretion. I use a suite of very high-resolution zoom-in cosmological simulations of galaxies in order to study the assembly of galaxies at high redshifts, z ≥ 2, to quantify the role of environment and of the parent DM halos in this procss. My models have been chosen to lie within similar mass DM halos, log(Mvir /Mo) ~ 11.65±0.05, which have been selected at the final redshifts of zf = 6, 4, and 2. Moreover, I have employed DM halos residing in high and low density environments in the universe, and invoked two different galactic wind feedbacks, for the future comparison. These preferences allows me to analyze how a different growth rate of these DM halos propagates down to galaxy scales, affecting their basic parameters. I model and analyze the morphology of the central, most massive galaxies in the parent DM halos, and determine the basic properties of these galaxies. I perform the decomposition of galaxies into the basic components: disks, bulges, and spheroids. Furthermore, I evaluate the properties of stellar bars which develop in these objects. Finally, this ulta-high resolution simulation data allows me to investigate the penetrating cold accretion filaments feeding the central galaxies. My main results can be divided into three groups. For galaxies, I find that (1) Although they evolve in different epochs, their global parameters (e.g., baryonic masses and sizes) remain within a narrow range. The galactic morphology, kinematics and stellar populations differ substantially, yet all of them host sub-kiloparsec stellar bars; (2) The star formation rates (SFRs) appear higher for larger zf, 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 zf. 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 point-spread-function (PSF)-degraded James Webb Space Telescope (JWST) images allow to detect stellar disks at all zf. 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 zf; (6) Finally, the Atacama Large Millimeter/Submillimeter Array (ALMA) images detect disks at all zf, but their spiral structure is only detectable in zf=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. For stellar bars, my conclusions are that (1) The high-z bars form in response to various perturbations, namely, mergers, close flybys, cold accretion inflows along the cosmological filaments, etc.; (2) These bars account for a large-mass fraction of the parent galaxies; (3) The bars display large corotation-to-bar size ratios and are weaker compared to their low-redshift counterparts, by measuring their Fourier amplitudes; (4) High-z bars are very gas-rich, and (5) Their pattern speed evolution does not exhibit the monotonic decline with time as a result of braking against the DM, as at low z; (6) The bar properties, including their stellar population (star formation rates and metal enrichment) depend sensitively on the prevailing feedback; (7) Finally, we find that bars can weaken substantially during cosmological evolution, becoming weak oval distortions — hence bars are destroyed and reformed multiple times unlike their low-z counterparts. Moreover, in all cases, the bars in our simulations have been triggered by interactions. For accretion flows onto the DM halos and galaxies, I have analyzed the thermodynamic and kinematic properties of cold gas accretion in filaments, from about three virial radii of the host DM halos and down to the circumgalactic regions, deep inside the halos. I have calculted the radial profiles of density, temperature, metallicity and the infall velocity of the filamentary gas. Specifically, I have focused on the dissolution of filaments inside the innermost ~ 30 h-1kpc, where the flow is subject to the Kelvin-Helmholtz instability due to the velocity gradient between the filament core and its envelope. This instability leads to ablation of the filament and generates turbulence in the region. I have quantified this turbulence, which can affect also the gas motions in the underlying galactic disks.

Digital Object Identifier (DOI)

Funding Information

This work has also been partially supported by the Hubble Theory grant HST-AR-14584, and by JSPS KAKENHI grant 16H02163 (to I.S.). The STScI is operated by the AURA, Inc., under NASA contract NAS5-26555. E.R.D. acknowledges support of the Collaborative Research Center 956, subproject C4, funded by the Deutsche Forschungsgemeinschaft (DFG). Simulations have been performed using generous allocation of computing time on the XSEDE machines under the NSF grant TG-AST190016, and by the University of Kentucky Lipscomb Computing Cluster.