High-Velocity Molecular Clouds in the Barred Spiral Galaxy M83

Gas in a disk galaxy is generally rotation dominated. However, some can deviate from this rotation due to feedback from massive stars, as well as inflows of gas from external sources or galactic fountains. These high-velocity clouds (HVCs) may play a critical role in galaxy evolution, potentially triggering star formation through cloud-cloud collisions and contributing to material circulation within galaxies. In the MW, the edge-on view complicates comprehensive studies of such HVCs. Detecting HVCs in nearby face-on galaxies are therefore essential. In this study, we focus on the barred spiral galaxy M83, where high spatial resolution, high-sensitivity CO (1–0) data (Koda et al. 2023) are available. We identified molecular clouds using the astrodendro (Rosolowsky et al. 2008) algorithm and searched for clouds with velocities deviating by more than 50 km/s from the large-scale velocity field as HVCs. A total of 10 HVCs were detected—nine redshifted and one blueshifted—clearly highlighting an asymmetry in their velocity distribution. These HVCs have radius of 30 –80 pc, masses of 10^4–10^5 Msun, and velocity dispersions of 3–20 km/s, displaying a tendency toward higher velocity dispersion compared to other molecular clouds in M83. Most of HVCs do not overlap with the candidates of supernova remnants, and the energy needed to drive HVCs at such high velocities exceeds supernova energy. We thus claim that most HVCs found in this study are inflow from outside the M83's disk.