Systematically Measuring Ultra Diffuse Galaxies in HI: Results from the Pilot Survey

We present neutral hydrogen (HI) observations using the Robert C. Byrd Green Bank Telescope (GBT) of 70 optically-detected UDG candidates in the Coma region from the Systematically Measuring Ultra-Diffuse Galaxies survey (SMUDGes). We detect HI in 18 targets, confirming 9 to be gas-rich UDGs and the remainder to be foreground dwarfs. None of our HI-detected UDGs are Coma Cluster members and all but one are in low-density environments. The HI-detected UDGs are bluer and have more irregular morphologies than the redder, smoother candidates not detected in HI, with the combination of optical color and morphology being a better predictor of gas richness than either parameter alone. There is little visual difference between the gas-rich UDGs and the foreground dwarfs in the SMUDGes imaging, and distances are needed to distinguish between them. We find that the gas richnesses of our HI-confirmed UDGs and those from other samples scale with their effective radii in two stellar mass bins, possibly providing clues to their formation. We attempt to place our UDGs on the baryonic Tully-Fisher relation (BTFR) using optical ellipticities and turbulence-corrected HI linewidths to estimate rotation velocities, but the potential systematics associated with fitting smooth $\mathrm{S\acute{e}rsic}$ profiles to clumpy, low-inclination low surface brightness disks precludes a meaningful analysis of potential BTFR offsets. These observations are a pilot for a large campaign now underway at the GBT to use the HI properties of gas-rich UDGs to quantitatively constrain how these galaxies form and evolve.Comment: Accepted by ApJ. Revisions include updated versions of Figures 3-9, new table 5, and expanded discussion. Conclusions unchanged. Figures 6-8 will be available in higher resolution in the published versio

2D Bayesian automated tilted-ring fitting of disk galaxies in large HI galaxy surveys: 2DBAT

We present a novel algorithm based on a Bayesian method for 2D tilted-ring analysis of disk galaxy velocity fields. Compared to the conventional algorithms based on a chi-squared minimisation procedure, this new Bayesian-based algorithm suffers less from local minima of the model parameters even with highly multi-modal posterior distributions. Moreover, the Bayesian analysis, implemented via Markov Chain Monte Carlo (MCMC) sampling, only requires broad ranges of posterior distributions of the parameters, which makes the fitting procedure fully automated. This feature will be essential when performing kinematic analysis on the large number of resolved galaxies expected to be detected in neutral hydrogen (HI) surveys with the Square Kilometre Array (SKA) and its pathfinders. The so-called '2D Bayesian Automated Tilted-ring fitter' (2DBAT) implements Bayesian fits of 2D tilted-ring models in order to derive rotation curves of galaxies. We explore 2DBAT performance on (a) artificial HI data cubes built based on representative rotation curves of intermediate-mass and massive spiral galaxies, and (b) Australia Telescope Compact Array (ATCA) HI data from the Local Volume HI Survey (LVHIS). We find that 2DBAT works best for well-resolved galaxies with intermediate inclinations (20 deg < i < 70 deg), complementing three-dimensional techniques better suited to modelling inclined galaxies.Comment: Accepted for publication in MNRAS; 46 pages, 33 figure

Modeling Non-Circular Motions in Disk Galaxies: Application to NGC 2976

We present a new procedure to fit non-axisymmetric flow patterns to 2-D velocity maps of spiral galaxies. We concentrate on flows caused by bar-like or oval distortions to the total potential that may arise either from a non-axially symmetric halo or a bar in the luminous disk. We apply our method to high-quality CO and Halpha data for the nearby, low-mass spiral NGC 2976 previously obtained by Simon et al., and find that a bar-like model fits the data at least as well as their model with large radial flows. We find supporting evidence for the existence of a bar in the baryonic disk. Our model suggests that the azimuthally averaged central attraction in the inner part of this galaxy is larger than estimated by these authors. It is likely that the disk is also more massive, which will limit the increase to the allowed dark halo density. Allowance for bar-like distortions in other galaxies may either increase or decrease the estimated central attraction.Comment: 12 pages, 6 figures, accepted for publication in ApJ. v2: minor changes to match proofs. For version with high-resolution figures, see http://www.physics.rutgers.edu/~spekkens/papers/noncirc.pd