Hunting for Anomalous Gas: Kinematic Modelling of Disk Galaxies in 2D and 3D

Abstract

Understanding disk galaxy kinematics is vital to understand how gas impacts their evolution. Different galaxy processes often occur simultaneously, from gradual, internally-driven secular processes, to hydrodynamic and gravitational cluster interactions such as ram pressure and tides. It is well-known that gas plays a vital role in galaxy evolution, however we can only infer this from theoretical models, galaxy morphologies, and parameters indicative of perturbation. Kinematic models to both 2D velocity fields and 3D data cubes can shed light on these processes and provide mechanistic interpretations for gas dynamics. Spiral galaxy kinematics are characterized by a thin-disk component in which material travels along circular orbits - deviations from this pattern indicate the presence of one or more of the aforementioned processes. We begin our investigation with the "HIghMass" galaxies, and test the late-accretion hypothesis for gas acquisition to explain their unusual gas-richness by modelling their velocity fields with DiskFit. We are able to deliver the rotation curves for four massive spiral galaxies, and characterize non-circular flows in two, but we are unable to observe a smoking gun for gas accretion. Next, we examine the Virgo Cluster, which is the preeminent laboratory for the study of galaxy clusters due to its relative proximity and lack of kinematic relaxation. We use KinMS to 3D model galaxy data cubes in both atomic and molecular gas to quantify the fraction of anomalous gas that deviates from rotation. Our analysis reveals that atomic gas is sytematically more anomalous than molecular gas, which is physically motivated because atomic gas is more diffuse and persists at larger galactocentric radii. We also find a wide range of anomalous fractions in otherwise morphologically symmetric galaxies in both gas phases, suggesting that 2D asymmetry metrics miss non-circular gas flow signatures. We also note a lag in the molecular gas anomalous fraction compared to atomic gas across morphological categories of increasing gas depletion, implying the discrepant influence that galaxy processes can have on different components. These analysis methods are scalable and are vital tools for modelling galaxy kinematics and quantifying non-circular flows in an era of large surveys and abundant resolved data products.