BASS. LI. Cool gas supply of HI-massive local Seyfert galaxies

We present neutral atomic hydrogen (H I) imaging observations of 22 H I-rich (MHI ≳ 109.7 M⊙), hard X-ray-selected local Seyferts to explore how cool gas is supplied to active galactic nuclei (AGN) hosts. The sample predominantly resides in group-like, gas-rich environments. About 80% (18/22) of the galaxies have H I-detected neighbors, 61% (11/18) of which clearly exhibit strong lopsidedness, one-sided gas tails, and/or gas structures connecting to nearby companion galaxies, suggesting gas exchange histories. We examine the H I size-mass relation and star formation properties of these H I-rich AGN hosts, finding no systematic deviations from known scaling relations. In most cases, our samples are the most massive systems within their respective groups, implying that our sample is more likely to acquire gas rather than lose it. Interestingly, galaxies with more extended H I disks show stronger AGN activity. Considering that extended H I is often associated with external processes, this finding suggests that environmentally accreted gas – through galaxy interactions and gas exchange with neighboring systems – may have played a role in supplying additional fuel to the AGNs in our sample. Notably, the H I extent–AGN activity correlation becomes even tighter for those AGN hosts whose neighboring galaxies are gas poor or lack H I, further supporting externally supplied gas as a fuel source.