The oxygen abundance deficiency in irregular galaxies

The observed oxygen abundances in a number of irregular galaxies have been compared with predictions of the closed-box model of chemical and photometr ic evolution of galaxies. Oxygen is found to be deficient with respect to t he predicted abundances. This is an indicator in favor of loss of heavy ele ments via galactic winds or/and of infall of low-abundance gas onto the gal axy. The oxygen abundance deficiency observed within the optical edge of a galax y cannot be explained by mixing with the gas envelope observed outside the optical limit. We confirm the widespread idea that a significant part of th e heavy elements is ejected by irregular galaxies in the intergalactic medi um.