We present a mass model for the Milky Way, which is fit to observations of the Sagittarius stream together with constraints derived from a wide range of photometric and kinematic data. The model comprises a Sérsic bulge, an exponential disk, and an Einasto halo. Our Bayesian analysis is accomplished using an affine-invariant Markov chain Monte Carlo algorithm. We find that the best-fit dark matter halo is triaxial with axis ratios of 3.3±0.7 and 2.7±0.4 and with the short axis approximately aligned with the Sun-Galactic centre line. Our results are consistent with those presented in Law and Majewski (2010). Such a strongly aspherical halo is disfavoured by the standard cold dark matter scenario for structure formation.

We examine different measures of asymmetry for galaxy H i velocity profiles. We introduce the channel-by-channel asymmetry and the velocity-of-equality statistics to quantify profile asymmetries. Using a sample of simulated galaxies, we examine how these and the standard lopsidedness morphometric statistic depend on a variety of observational effects, including the viewing angle and inclination. We find that our newly introduced channel-by-channel asymmetry is less sensitive to the effects of viewing angle and inclination than other morphometrics. Applying our statistics to the WHISP (Westerbork H i survey of Irregular and SPiral galaxies) H i galaxy sample, we also find that the channel-by-channel asymmetry is a better indicator of visually classified asymmetric profiles. In addition, we find that the lopsidedness–velocity of equality space can be used to identify profiles with deep central dips without visual inspection.

The observed velocities of the gas in barred galaxies are a combination of the azimuthallyaveraged circular velocity and non-circular motions, primarily caused by gas streaming along the bar. These non-circular flows must be accounted for before the observed velocities can be used in mass modeling. In this work, we examine the performance of the tilted-ring method and the DiskFit algorithm for transforming velocity maps of barred spiral galaxies into rotation curves (RCs) using simulated data. We find that the tilted-ring method, which does not account for streaming motions, under/over-estimates the circular motions when the bar is parallel/perpendicular to the projected major axis. DiskFit, which does include streaming motions, is limited to orientations where the bar is not-aligned with either the major or minor axis of the image. Therefore, we propose a method of correcting RCs based on numerical simulations of galaxies. We correct the RC derived from the tilted-ring method based on a numerical simulation of a galaxy with similar properties and projections as the observed galaxy. Using observations of NGC 3319, which has a bar aligned with the major axis, as a test case, we show that the inferred mass models from the uncorrected and corrected RCs are significantly different. These results show the importance of correcting for the non-circular motions and demonstrate that new methods of accounting for these motions are necessary as current methods fail for specific bar alignments..

We present results from our analysis of the Hydra I cluster observed in neutral atomic hydrogen (H i) as part of the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY). These WALLABY observations cover a 60-square-degree field of view with uniform sensitivity and a spatial resolution of 30 arcsec. We use these wide-field observations to investigate the effect of galaxy environment on H i gas removal and star formation quenching by comparing the properties of cluster, infall and field galaxies extending up to ∼5R200 from the cluster centre. We find a sharp decrease in the H i-detected fraction of infalling galaxies at a projected distance of ∼1.5R200 from the cluster centre from $\sim 0.85\%$ to $\sim 0.35\%$. We see evidence for the environment removing gas from the outskirts of H i-detected cluster and infall galaxies through the decrease in the H i to r-band optical disc diameter ratio. These galaxies lie on the star forming main sequence, indicating that gas removal is not yet affecting the inner star-forming discs and is limited to the galaxy outskirts. Although we do not detect galaxies undergoing galaxy-wide quenching, we do observe a reduction in recent star formation in the outer disc of cluster galaxies, which is likely due to the smaller gas reservoirs present beyond the optical radius in these galaxies. Stacking of H i non-detections with H i masses below $M_{\rm {HI}}\lesssim 10^{8.4}\, \rm {M}_{\odot }$ will be required to probe the H i of galaxies undergoing quenching at distances ≳ 60 Mpc with WALLABY.