Modeling Evolution of Galactic Bars at Cosmic Dawn
  We study evolution of galactic bars using a suite of very high-resolution
zoom-in cosmological simulations of galaxies at high redshifts, z ~ 9-2. Our
models have been chosen to lie within similar mass dark matter (DM) halos,
log(Mvir}/Mo)~ 11.65 +/- 0.05, at redshifts 6, 4, and 2, in high and low
overdensity environments. We apply two galactic wind feedback mechanisms for
each galaxy model. All galaxies develop sub-kpc stellar bars which differ in
their properties. We find 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. In summary, stellar bars appear to be not
only a contemporary phenomenon, but based on the increased frequency of
mergers, flybys and the strength of cold accretion flows at high $z$, we expect
them to be ubiquitous at redshifts > 2 -- the epoch of a rapid galaxy growth
and larger stellar dispersion velocities.
