On the effective oxygen yield in the disks of spiral galaxies
The factors that influence the chemical evolution of galaxies are poorly understood. Both gas inflow and gas outflow reduce the gas-phase abundance of heavy elements (metallicity), whereas ongoing star formation continuously increases it. To exclude the stellar nucleosynthesis from consideration, we analyze for a sample of 14 spiral galaxies the radial distribution of the effective yield of oxygen y{sub eff}, which would be identical to the true stellar yield (per stellar generation) y{sub o} if the evolution followed the closed-box model. As the initial data for gas-phase abundance, we used the O/H radial profiles from Moustakas et al., based on two different calibrations (the PT2005 and KK2004 methods). In most of the galaxies with the PT2005 calibration, which we consider the preferred one, the yield y{sub eff} in the main disk (R⩾0.2 R{sub 25}, where R{sub 25} is the optical radius) increases with radius, remaining lower than the empirically found true stellar yield y{sub o}. This may indicate the inflow of less-enriched gas predominantly to the inner disk regions, which reduces y{sub eff}. We show that the maximal values of the effective yield in the main disks of galaxies, y{sub eff,max}, anticorrelate with the total mass of galaxies and with the mass of their dark halos enclosed within R{sub 25}. It allows us to propose the greater role of gas accretion for galaxies with massive halos. We also found that the radial gradient of oxygen abundance normalized to R{sub 25} has a tendency to be shallower in the systems with lower dark halo to stellar mass ratio within the optical radius, which, if confirmed, gives evidence of the effective radial mixing of gas in galaxies with a relatively light dark matter halo.