Numerical simulations of expanding supershells in dwarf irregular galaxies

Numerical hydrodynamical modelling of supernova-driven shell formation is performed with a purpose to reproduce a giant HI ring (diameter 1.7 kpc) in the dwarf irregular galaxy Holmberg I (Ho I). We find that the contrast in HI surface density between the central HI depression and the ring is sensitive to the shape of the gravitational potential. This circumstance can be used to constrain the total mass (including the dark matter halo) of nearly face-on dwarf irregulars. We consider two models of Ho I, which differ by an assumed mass of the dark matter halo Mh. The contrast in HI surface density between the central HI depression and the ring, as well as the lack of gas expansion in the central hole, are better reproduced by the model with a massive halo of $M_{\rm h}=6.0\times 10^9~M_{\odot}$ than by that with a small halo of $M_{\rm h}=4.0\times 10^8~M_{\odot}$, implying that Ho I is halo-dominated. Assuming the halo mass of $6.0\times 10^9~M_{\odot}$, we determine the mechanical energy required to form the observed ring equal to $(3.0 \pm 0.5) \times 10^{53}$ ergs, equivalent $300\pm 50$ Type II supernovae. The inclination of Ho I is constrained to $15^\circ{-}20^\circ$ by comparing the modelled HI spectrum and channel maps with those observed