Kinematic and dynamics of the galaxy ESO 358-60

TL;DR

This study uses the Velocity Ring Model to analyze the kinematic structure of galaxy ESO 358-60, revealing dominant tangential motions in the center, significant radial motions outward, and questioning the warp inferred by the Tilted Ring Model.

Contribution

It introduces the VRM as an alternative to TRM for galaxy kinematic analysis and demonstrates its effectiveness in revealing disk structures and correcting warp artifacts.

Findings

VRM shows tangential motions dominate inner regions

Radial motions increase toward galaxy outskirts

DMD model suggests lower galaxy mass, fitting rotation curves better

Abstract

We investigate the velocity field derived from HI measurements of the irregular galaxy ESO 358-60 using the Velocity Ring Model (VRM) method. This technique, which assumes a coplanar disk, allows us to reconstruct coarse-grained maps of both radial and tangential velocity components from the observed line-of-sight velocity field. Such maps reveal that tangential motions dominate the inner regions, while radial motions become increasingly significant toward the outskirts. This kinematic behavior contrasts with that inferred from the Tilted Ring Model (TRM), which suggests that radial motions are more prominent in the intermediate disk and negligible in the outskirts and detects a pronounced warp of approximately $20^\circ$, with the inner disk nearly edge-on and the outer regions inclined by approximately $60^\circ$. In contrast, the VRM analysis finds that the disk exhibits a bar-like structure in its central regions. This interpretation is further supported by the intensity and velocity dispersion maps. To test the origin of the TRM-derived warp, we construct a toy model based on the TRM results and analyze it with the VRM technique, finding evidence that the warp is likely an artifact arising from the TRM's assumptions. Finally, we estimate the galaxy's mass using both the standard dark matter halo model and a dark matter disk (DMD) model, where all mass lies in the disk plane. The DMD yields a total mass approximately three times lower and provides a slightly better fit to the rotation curve.