Modeling Evolution of Galactic Bars at Cosmic Dawn

We study the evolution of galactic bars using a suite of very high-resolution zoom-in cosmological simulations of galaxies at z similar to 9-2. Our models were chosen to lie within similar-mass dark matter (DM) halos, log(M (vir)/M (circle dot)) similar to 11.65 +/- 0.05, at z = 6, 4, and 2, in high- and low-overdensity environments. We apply two galactic wind feedback mechanisms for each model. All galaxies develop subkiloparsec stellar bars differing in their properties. We find that (1) the high-z bars form in response to various perturbations: mergers, close flybys, cold accretion inflows along the cosmological filaments, etc.; (2) these bars account for the large mass fraction of galaxies; (3) bars display large corotation-to-bar size ratios, are weaker compared to their low-redshift counterparts by measuring their Fourier amplitudes, and are very gas-rich; (4) their pattern speed does not exhibit monotonic decline with time owing to braking against DM, as at low z; (5) bar properties, including their stellar population (star formation rates and metal enrichment), depend sensitively on prevailing feedback; and (6) bars can weaken substantially during cosmological evolution, becoming weak oval distortions-hence bars are destroyed and reformed multiple times, unlike their low-z counterparts. In all cases, bars in our simulations have been triggered by interactions. In summary, not only do stellar bars appear to be a contemporary phenomenon, but based on increased frequency of mergers, flybys, and the strength of cold accretion flows at high z, we also expect them to be ubiquitous at redshifts greater than or similar to 2-the epoch of rapid galaxy growth and larger stellar dispersion velocities.