Importance of Initial Condition on Bar Secular Evolution: Role of Halo Angular Momentum Distribution Discontinuity

TL;DR

This paper investigates how the initial distribution of angular momentum in dark matter halos influences the long-term evolution of bars in disk galaxies, revealing that more continuous distributions lead to stronger bars and more pronounced bulges.

Contribution

It introduces the importance of the halo angular momentum distribution discontinuity as a key initial condition affecting bar evolution in galaxy simulations.

Findings

Bars form in all models after a few Gyr.

More continuous halo angular momentum distributions lead to stronger bars.

Halo angular momentum distribution impacts bulge shape and prominence.

Abstract

The dark matter halo properties, for example, mass, spin and concentration play a significant role in the formation and evolution of bars in disk galaxies. This study highlights the importance of a new parameter: the dark matter halo angular momentum distribution in the central region of disk. We experiment with N-body galaxy models having a disk and dark matter similar to Milky Way-type galaxies. In these models, we vary the discontinuity of the angular momentum distribution of the halo (the total spin is the same for all models). Our N-body experiments suggest that bar forms in all models after a few Gyr of disk evolution. However, in the secular evolution of the bar, as we evolve these models until 9.78 Gyr, the bar gains its strength in the model with the most continuous halo angular momentum distribution, and the bar loses strength for the most discontinuous halo angular momentum distribution. The secular evolution of the bar suggests that box/peanut/x-shaped bulges similar to those found in the Milky Way disk should be more pronounced in halos with continuous halo angular momentum distributions. This study demonstrates the importance of the initial condition setup of galaxy systems, namely the discontinuity in the dark matter halo angular momentum distribution for a given density distribution, on the bar secular evolution in the disk galaxy simulations. Further, this study helps reconcile the conflicting results of bar secular evolution in a high-spinning halo of the recent literature.