Numerical simulations of expanding supershells in dwarf irregular galaxies

I. Application to Holmberg I

¹ Institute of Physics, Stachki 194, Rostov-on-Don, Russia, and Isaac Newton Institute of Chile, Rostov-on-Don Branch
² Radioastronomisches Institut der Universitt Bonn, Auf dem Hgel 71, 53121 Bonn, Germany e-mail: uklein@astro.uni-bonn.de
³ Rostov University, Sorge 5, Rostov-on-Don, Russia, and Isaac Newton Institute of Chile, Rostov-on-Don Branch e-mail: yus@phys.rsu.ru
⁴ CSIRO Australia Telescope National Facility, Cnr Vimiera & Pembroke Roads, Marsfield NSW 2122, Australia e-mail: Juergen.Ott@csiro.au

Corresponding author: E. I. Vorobyov, eduard_vorobev@mail.ru

Received: 14 April 2003
Accepted: 22 September 2003

Abstract

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 M_h. 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 than by that with a small halo of , implying that Ho I is halo-dominated. Assuming the halo mass of , we determine the mechanical energy required to form the observed ring equal to  ergs, equivalent Type II supernovae. The inclination of Ho I is constrained to by comparing the modelled HI spectrum and channel maps with those observed.