The Neutral Gas Dynamics of the Nearby Magellanic Irregular Galaxy UGCA 105
We present new low-resolution H I spectral line imaging, obtained with the Karl G. Jansky Very Large Array, of the star-forming Magellanic irregular galaxy UGCA 105. This nearby ( D = 3.39 ± 0.25 Mpc), low-mass ( 4.3 ± 0.5 × 10 8 M ☉ ) system harbors a large neutral gas disk (H I radius ~7.2 kpc at the = 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 –1 , 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) × 10 9 M ☉ , is ~10 times as large as the luminous baryonic components (neutral atomic gas and stars). The proximity and favorable inclination (55°) 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.