The Rapid Onset of Stellar Bars in the Baryon-dominated Centers of Disk Galaxies

• DOI: 10.3847/1538-4357/acc469
• Publication Date: 2023-04-25T12:01:05Z
• Authors: Joss Bland-Hawthorn; Thor Tepper-Garcia; Oscar Agertz; Ken Freeman
• Keywords: 0301 basic medicine; FOS: Physical sciences; Milky Way formation; Astrophysics; Milky Way evolution; Astrophysics - Astrophysics of Galaxies; 01 natural sciences; QB460-466; 03 medical and health sciences; Astrophysics of Galaxies (astro-ph.GA); Milky Way Galaxy physics; 0103 physical sciences; Galaxy bars; Disk galaxies; Milky Way dynamics

Abstract Recent observations of high-redshift galactic disks (z ≈ 1–3) show a strong negative trend in the dark-matter (DM) fraction f DM with increasing baryon surface density. For this to be true, the inner baryons must dominate over DM in early massive galaxies, as observed in the Milky Way today. If disks are dominant at early times, we show that stellar bars form promptly within these disks, leading to a high bar fraction. New James Webb Space Telescope observations provide the best evidence for mature stellar bars in this redshift range. The disk mass fraction f disk within R

s = 2.2 R disk is the dominant factor determining how rapidly a bar forms. Using 3D hydro simulations of halo-bulge-disk galaxies, we confirm the “Fujii relation” for the exponential dependence of the bar formation time τ bar as a function of f disk. For f disk > 0.3, the bar formation time declines exponentially fast with increasing f disk. Instead of Fujii's arbitrary threshold for when a bar appears, for the first time, we exploit the exponential growth timescale associated with the positive feedback cycle as the bar emerges from the underlying disk. A modified, mass-dependent trend is observed for halos relevant to systems at cosmic noon (

10.5 < log

M

halo

< 12

), where the bar onset is slower for higher-mass halos at a fixed f disk. If baryons dominate over DM within R ≈ R

s , we predict that a high fraction of bars will be found in high-redshift disks long before z = 1.