The Neutral Gas Dynamics of the Nearby Magellanic Irregular Galaxy UGCA 105

TL;DR

This study uses new HI spectral line imaging to analyze the neutral gas dynamics of the nearby Magellanic irregular galaxy UGCA 105, revealing its large gas disk, rotation curve, and mass distribution.

Contribution

First detailed rotation curve and dynamical mass measurement of UGCA 105 using tilted ring models from JVLA HI data.

Findings

Rotation velocity flattens at 72 km/s.

Dynamical mass is approximately 10 times the baryonic mass.

Neutral gas disk extends twice as far as the stellar disk.

Abstract

We present new low-resolution HI spectral line imaging, obtained with the Karl G. Jansky Very Large Array (JVLA), of the star-forming Magellanic irregular galaxy UGCA 105. This nearby (D = 3.39+/-0.25 Mpc), low mass [M_HI=(4.3+/-0.5)x10^8 Solar masses] system harbors a large neutral gas disk (HI radius ~7.2 kpc at the N_HI=10^20 cm^-2 level) that is roughly twice as large as the stellar disk at the B-band R_25 isophote. We explore the neutral gas dynamics of this system, fitting tilted ring models in order to extract a well-sampled rotation curve. The rotation velocity rises in the inner disk, flattens at 72+/-3 km/s, and remains flat to the last measured point of the disk (~7.5 kpc). The dynamical mass of UGCA 105 at this outermost point, (9+/-2)x10^9 Solar masses, is ~10 times as large as the luminous baryonic components (neutral atomic gas and stars). The proximity and favorable inclination (55 degrees) of UGCA 105 make it a promising target for high-resolution studies of both star formation and rotational dynamics in a nearby low-mass galaxy.