The response of the inner dark matter halo to stellar bars

TL;DR

This study investigates how stellar bars in galaxies influence the shape and density of the surrounding dark matter halo, revealing a strong correlation between stellar and halo bar properties through simulations.

Contribution

It characterizes the structure of halo bars and their relation to stellar bars using simulations, including effects of gas, star formation, and live versus frozen stellar potentials.

Findings

Halo bars follow the trends of stellar bars.

Stronger stellar bars correlate with stronger halo bars.

Live stellar bars induce a more pronounced dark matter response.

Abstract

Barred galaxies constitute about two thirds of observed disc galaxies. Bars affect not only the mass distribution of gas and stars, but also that of the dark matter. An elongation of the inner dark matter halo is known as the halo bar. We aim to characterise the structure of the halo bars, with the goal of correlating them with the properties of the stellar bars. We use a suite of simulated galaxies with various bar strengths, including gas and star formation. We quantify strengths, shapes, and densities of these simulated stellar bars. We carry out numerical experiments with frozen and analytic potentials in order to understand the role played by a live responsive stellar bar. We find that the halo bar generally follows the trends of the disc bar. The strengths of the halo and stellar bars are tightly correlated. Stronger bars induce a slight increase of dark matter density within the inner halo. Numerical experiments show that a non-responsive frozen stellar bar would be capable of inducing a dark matter bar, but it would be weaker than the live case by a factor of roughly two.