Dark Matter Halos and Evolution of Bars in Disk Galaxies: Collisionless Models Revisited

TL;DR

This study uses collisionless models of stellar disks in live dark matter halos to analyze bar evolution, highlighting the halos' dual role in slowing and facilitating angular momentum transfer during different evolutionary phases.

Contribution

The paper provides a detailed quantification of dark matter halos' dual influence on bar dynamics and introduces the corotation-to-disk size ratio as a key indicator of bar evolution stages.

Findings

Centrally concentrated halos inhibit dynamical processes and slow angular momentum transfer.

Disk angular momentum remains nearly constant within corotation radius when Rcr is inside the disk.

Bar pattern speed can stall when corotation radius moves outside the disk.

Abstract

We construct and evolve families of steady-state models of stellar disks embedded in live DM halos, in order to study the dynamical and secular phases of bar evolution. These models are tested against those published in the literature in order to extend them and include the gaseous component in the follow up paper. We are interested in the angular momentum (J) redistribution in the disk-halo system. We confirm the previous results and quantify for the first time the dual role that the DM halos play in the bar evolution: more centrally concentrated halos dilute the dynamical processes, such as spontaneous bar instability and vertical buckling instability, and slowdown the J transfer, while facilitating it in the secular phase. Within the corotation radius (Rcr), the disk J remains nearly constant, as long as Rcr stays within the disk -- a sign that the lost J to the outer disk and the halo is being compensated by an influx of fresh J due to the outward motion of Rcr. This is feasible as long as the bar slowdown dominates the loss of J inside Rcr. We find that in some models the bar pattern speed stalls for prolonged time periods when Rcr is located outside the disk. This phenomenon appears concurrent with the near absence of J transfer between the disk and the halo. Furthermore, we confirm that stellar bars generally display the corotation to bar size ratios in the range of ~1-1.4, but only between the times of the first buckling and Rcr leaving the disk. The corotation-to-disk size ratio emerges as an important dynamic discriminator between various stages of barred disk evolution. Finally, we analyze a number of correlations between the basic parameters of a barred disk and a halo, some already reported in the literature and some new.