© Sushma Kurapati

Galaxy evolution is intricately linked to the availability of gas for accretion and the surrounding environment at both local and global scales. Galaxies require a continuous gas supply to sustain star formation, yet the dominant mechanisms—whether galactic fountains, infalling satellites, or cold accretion from the cosmic web—remain uncertain. In low-density voids at z ~ 0, cold gas accretion is expected to dominate, delivering gas via filamentary substructures. Neutral hydrogen (HI) observations provide a unique window into these processes, tracing both large-scale galaxy distributions and gas dynamics within the interstellar medium (ISM), including accretion. This talk presents three HI studies that probe distinct aspects of gas accretion. First, using 440 MeerKAT pointings from the SARAO MeerKAT Galactic Plane Survey, we investigate the Local Void, the nearest large underdense region. In the absence of optical data, HI observations allow us to map its substructure and extent, revealing filamentary galaxy alignments that may serve as potential accretion pathways. Second, GMRT HI observations of extremely metal-poor dwarf galaxies in voids uncover disrupted HI morphologies and misaligned gas-stellar disks, likely due to ongoing cold gas accretion from void filaments. Their isolation and low metallicities further support external accretion as a key driver of their evolution. Finally, ultra-deep HI 21 cm observations from the MHONGOOSE survey of the edge-on galaxy UGCA 250 reveal an extensive extraplanar gas reservoir, including a large HI tail, a counter-rotating cloud, and multiple satellite galaxies. A detailed tilted-ring model reveals a thick HI disk structure, with our analysis suggesting a mixed origin for the extraplanar gas, likely arising from a combination of internal stellar feedback and tidal interactions. Together, these studies offer new insights into gas accretion and regulation across cosmic environments, from large-scale void filaments to individual galaxy halos.