The neutral gas dynamics of the nearby magellanic irregular galaxy UGCA 105

Abstract

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 UGCA105. 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 ± 3kms -1, and remains flat to the last measured point of the disk (∼7.5 kpc). The dynamical mass of UGCA105 at this outermost point, (9 ± 2) × 10 9 M ⊙, is ∼ 10times as large as the luminous baryonic components (neutral atomic gas and stars). The proximity and favorable inclination (55°) of UGCA105 make it a promising target for high-resolution studies of both star formation and rotational dynamics in a nearby low-mass galaxy. © © 2012. The American Astronomical Society. All rights reserved.