SHIELD: Star Formation from WIYN and GALEX Imaging

Using images from the GALEX (Galaxy Evolution Explorer) GR6 pipeline (released 2010), as well as the WIYN 3.5m Observatory, we present a survey of the twelve SHIELD galaxies in the far-ultraviolet (FUV, 1500 Å) and near-ultraviolet (NUV, 2200 Å) filters. FUV data were available for eleven of the galaxies, AGC 749237 being the exception. Aperture photometry was performed on each image to determine the AB magnitude in the FUV and NUV filters.These values were then used to calculate flux, luminosity, and star formation rates (SFRs). Similarly, Hα images of each galaxy from WIYN (omitting AGC 749241) were analyzed to determine an SFR from Hα tracers. A comparison of the two star formation indicators for these galaxies suggests the presence of an Hα detriment, and supports previous findings regarding refined conversions for SFRs in extremely low-mass dwarfs

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

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.Comment: The Astronomical Journal, in pres