Massive Supernovae and Metallicity Boundary in Dwarf Galaxies

The increase of metallicity in the galactic interstellar medium occurs via the interaction of many physical processes. These processes differ by mass and chemical composition of the matter delivered into the interstellar medium. Massive supernovae have masses from 8 to 100 M_ and, during their explosions, eject the maximum amount of heavy elements into the surrounding space. The consequences of such outbursts are most easily detected in galaxies having the lowest masses. Based on the relationship between the luminosities of galaxies and their brightest stars, as well as theoretical models of massive supernovae and isochrones of stars with masses of 8.3–8.7 M_ , we determined that galaxies with luminosities below MB≥-12m.5 should be devoid of stars with masses greater than 8 M_ . This means that massive supernovae cannot form in such galaxies. Hence, the galaxies are deprived of their main source of metal enrichment. This constraint should be observed as a metallicity drop in galaxies at MB=-12m.5 . Based on the published data, a ‘‘luminosity–metallicity’’ diagram has been constructed, which indeed shows a metallicity jump at luminosities above MB=-12m.5 . In galaxies of even lower luminosity, massive supernovae never flare up and the metallicity of the interstellar medium increases due to the stellar wind and thermal pulsations of AGB (TP-AGB) stars.