On the effective oxygen yield in the disks of spiral galaxies
  The factors influencing chemical evolution of galaxies are poorly understood.
Both gas inflow and gas outflow reduce a gas-phase abundance of heavy elements
(metallicity) whereas the ongoing star formation continuously increases it. To
exclude the stellar nucleosynthesis from consideration, we analyze for the
sample of 14 spiral galaxies the radial distribution of the effective yield of
oxygen $y_{eff}$, which would be identical to the true stellar yield (per
stellar generation) $y_o$ 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, Kennicutt, Tremonti et al. (2010), based on two different
calibrations (Pilyugin & Thuan 2005 (PT2005) and Kobulnicky & Kewley 2004
(KK2004) methods). In most of galaxies with the PT2005 calibration, which we
consider as a preferred one, the yield $y_{eff}$ in the main disk ($R \ge
0.2~R_{25}$, where $R_{25}$ is the optical radius) increases with radius,
remaining lower than the empirically found true stellar yield $y_o$. This may
indicate the inflow of low-enriched gas predominantly to the inner disk
regions, which reduces $y_{eff}$.
  We show that the maximal values of the effective yield in the main disks of
galaxies, $y_{eff,max}$, anti-correlate with the total mass of galaxies and
with the mass of their dark halo enclosed within $R_{25}$. It allows to propose
the higher role of gas accretion for galaxies with massive halos. We also found
that the radial gradient of oxygen abundance normalized to $R_{25}$ 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 evidences of the
effective radial mixing of gas in galaxies with the relatively light dark
matter halo.
