SELECTIVE LOSS OF METALS FROM LOW-MASS GALAXIES

The fate of metals produced by Type II supernovae occurring at time intervals of order 106 yr in a low-mass, gas-rich disk galaxy have been studied via a numerical model. Two-dimensional hydrodynamic simulations were made for a typical stellar OB association located near the center of a model disk galaxy with a mass of 1.4 × 109 M⊙. Consistent with earlier studies, multiple SN led first to the production of a supershell and later to a galactic chimney which channels supernova debris out from the disk. Chimney development is aided by the low metallicity (Z = 0.1 Z⊙) of the model which depresses cooling rates. The simulation demonstrates that for this model galaxy approximately two-thirds of the metals ejected from SN in average OB associations will escape. This process is likely to be a factor in producing the observed mass-metallicity correlation in low-mass irregular galaxies.