Numerical simulations of expanding supershells in dwarf irregular galaxies

Free access article

Issue		A&A Volume 413, Number 3, January III 2004


Page(s)		939 - 948
Section		Stellar clusters and associations
DOI		http://dx.doi.org/10.1051/0004-6361:20031523

A&A 413, 939-948 (2004)
DOI: 10.1051/0004-6361:20031523

I. Application to Holmberg I

E. I. Vorobyov¹, U. Klein², Yu. A. Shchekinov³ and J. Ott⁴

¹ Institute of Physics, Stachki 194, Rostov-on-Don, Russia, and Isaac Newton Institute of Chile, Rostov-on-Don Branch
² Radioastronomisches Institut der Universit ${\rm\ddot a}$ t Bonn, Auf dem H ${\rm\ddot u}$ gel 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

(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 $M_{\rm h}$ . 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 $M_{\rm h}=6.0\times 10^9~M_{\odot}$ 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.

Key words: galaxies: dwarf -- individual: Holmberg I=DDO 63 -- ISM: bubbles

Offprint request: E. I. Vorobyov, eduard_vorobev@mail.ru

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