Dissecting Bar-Induced Stellar Kinematics in Disk Galaxies: The Bisymmetric Model and Rotation Curve Modifications

TL;DR

This study uses N-body simulations to analyze how galactic bars influence stellar kinematics and rotation curves, revealing characteristic velocity patterns and the impact of bar strength on galaxy dynamics.

Contribution

It introduces a detailed analysis of bar-induced stellar kinematic features and their effects on rotation curves, extending the bisymmetric model to include bar strength variations.

Findings

Stars on bar-supporting orbits show characteristic velocity patterns.

Bars increase radial pressure gradients and reduce rotational velocities.

Bar strength correlates with the magnitude of kinematic perturbations.

Abstract

We analyze bars formed in $N$-body simulations to investigate two key aspects of stellar kinematic structure of barred galaxies: the angular distributions of the radial and azimuthal components of stellar velocities, and the impact of bars on rotation curves. We find that stars on bar-supporting $x_1$-like orbits exhibit characteristic sawtooth-like radial velocity patterns and arch-like tangential velocity patterns as a function of azimuth. In contrast, stars on box and disk orbits show little azimuthal variation, effectively smoothing the overall velocity distribution. When averaged over all orbital families, the resulting kinematics are broadly consistent with the bisymmetric model of Spekkens & Sellwood, with the amplitudes of bar-induced velocity perturbations increasing with bar strength. In addition, bars amplify the radial pressure gradient associated with enhanced random stellar motions, leading to a noticeable reduction in the mean rotational velocity. This effect becomes more pronounced with increasing bar strength, resulting in a shallower rotation curve within the bar region. We discuss our results in the context of the kinematic properties of observed barred galaxies.