Probing Signals of Self-Interacting Dark Matter Core Collapse in HI-Rich Galaxies

We analyze rotation curves of five HI-rich galaxies recently discovered with MeerKAT. These galaxies exhibit sharply rising rotation curves, while their baryonic components are not dynamically dominant, suggesting that their dark matter halos have high inner densities. When fitting the standard Navarro-Frenk-White (NFW) halo model, four galaxies require extremely high halo concentrations, exceeding the cosmological median by $5\sigma$. In contrast, self-interacting dark matter (SIDM) halos in the core-collapse phase naturally account for the high densities in these galaxies. For halos with masses around $10^{11}~{\rm M_\odot}$, those in cosmic filaments exhibit concentrations consistent with the cosmological average, while halos in cosmic nodes show relatively higher concentrations that align with the SIDM fits but remain insufficient for the NFW fits. Our analysis indicates that these HI-rich galaxies may have formed in cosmic nodes of dark matter with significant self-interactions.