Modeling Non-Circular Motions in Disk Galaxies: A Bar in NGC 2976

TL;DR

This paper introduces a new model for non-circular motions in disk galaxies, attributing them to bar-like distortions, and applies it to NGC 2976, revealing a significant baryonic influence on the galaxy's potential.

Contribution

The paper presents a novel non-epicycle model for galaxy velocity fields that accounts for bar-like distortions, improving fit quality and providing insights into galaxy mass distribution.

Findings

Model fits CO and Halpha kinematics well

NGC 2976 likely hosts a bar structure

Baryonic matter significantly influences galaxy potential

Abstract

We give a brief description of a new model for non-circular motions in disk galaxy velocity fields, that does not invoke epicycles. We assume non-circular motions to stem from a bar-like or oval distortion to the potential, as could arise from a triaxial halo or a bar in the mass distribution of the baryons. We apply our model to the high-quality CO and Halpha kinematics of NGC 2976 presented by Simon et al. 2003; it fits the data as well as their model with unrealistic radial flows, but yields a steeper rotation curve. Our analysis and other evidence suggests that NGC 2976 hosts a bar, implying a large baryonic contribution to the potential and thus limiting the allowed dark matter halo density.