Oxygen abundance in nearby galaxies based on the spectra of H II regions from the Sloan Digital Sky Survey II: The interacting galaxies NGC 4631 and NGC 4656

The oxygen abundances in the interacting galaxies NGC 4631 and NGC 4656 have bee determined. The spectra of seven H II regions (four in NGC 4631 and three in NGC 4656) that exhibit the auroral [O III] λ436.3 nm line have been found in the SDSS II (Sloan Digital Sky Survey II) database. The intensities of spectral lines have been measured and the oxygen abundances in the H II regions have been determined. The central oxygen abundance and the radial gradient of its distribution in the disks of these galaxies have been estimated. The positions of the galaxies on the luminosity-metallicit diagram are examined.     

Oxygen abundances in the most oxygen-rich spiral galaxies

Oxygen abundances in the spiral galaxies expected to be richest in oxygen are estimated. The new abundance determinations are based on the recently discovered ff relation between auroral and nebular oxygen-line fluxes in high-metallicity H  ii regions. We find that the maximum gas-phase oxygen abundance in the central regions of spiral galaxies is 12+log(O/H) ∼ 8.75. This value is significantly lower (by a factor of ≳5) than the previously accepted value. The central oxygen abundance in the Milky Way is similar to that in other large spirals.