Global Evolution of Spiral Galaxies by Means of Cumulative Oxygen Abundances

Studying the global evolution of spiral galaxies requires determining their overall chemical compositions. However, since spirals tend to possess gradients in their chemical compositions, determining their overall chemical abundances poses a challenge. In this study, the framework for a newly proposed method for determining the overall oxygen abundance of a disk is established. By separately integrating the absolute amounts of hydrogen and oxygen out to large radii, the overall oxygen abundance is shown to reach an asymptotic value. In this manner, a reliable account of the overall chemical state is revealed. Knowing the chemical state of spirals then allows for their study alongside other galaxies, such as dwarf irregulars, whose chemical states are better understood. The relationship between the gas fraction and the overall oxygen abundance is established, and a comparison is made to the corresponding relationship for dwarf irregular galaxies. It is concluded that the effective oxygen yield for spirals is consistent with recent closed-box model estimates of yields for dwarf irregulars. Thus, it appears that the galaxy type does not have an effect on the formation of stars or the enrichment process associated with them, and no relation between yield and metallicity exists.