MeerKAT discovery of an infalling cold gas tail on to the nearby barred spiral galaxy, NGC 5643

ABSTRACT The detailed study of gas flows in local active galactic nuclei (AGN) is essential for understanding the regulation of star formation and black hole growth, which are fundamental to galaxy evolution. One such AGN case study is NGC 5643, a nearby ($D_{L}\sim 17.3$ Mpc) star-forming, late-type, Seyfert galaxy, where inflows and outflows have been observed in detail. NGC 5643 has been studied at multiple wavelengths; however, a key missing component is sensitive, high-resolution neutral hydrogen (H i) observations. We present 21-cm observations of NGC 5643 with MeerKAT, revealing six low-H i mass ($M_{\rm{H {\small I}}}\sim 10^{7}$ M$_\odot$) sources surrounding NGC 5643 and H i in IC 4444, $\sim 230$ kpc north of NGC 5643. In NGC 5643, H i extends beyond the stellar disc with several morphological and kinematical asymmetries. North of the disc is an extended 30 kpc tail with counterrotating velocities. This is H i gas accreting on to the regularly rotating disc of NGC 5643 from the environment. Within the spiral arms of the disc, we identify extraplanar gas components, tracing galactic fountains driven by star formation regions. These fountains have a molecular gas component and show an increased H$_{2}$/H i ratio. In the circum-nuclear region, we observe spatially unresolved H i absorption that is slightly blue-shifted ($\sim 72$ km s$^{-1}$) with an H i emission counterpart at red-shifted velocities. These MeerKAT observations provide a complete census of the H i in and around this nearby Seyfert galaxy, providing missing information on the cold gas flows fuelling the star formation and nuclear activity.