2000ApJ...538..141M

Result. of emission-line spectrophotometry of 68 H II regions in the strongly barred spiral galaxy NGC 7479 obtained with the Multi-Object Spectrograph at the Canada-France-Hawaii Telescope are presented. The average nebular extinction across the galaxy disk is A_v∼1.1 mag. There is a radial trend (-0.042±0.010 mag.kpc^–1) in the values of reddening suggesting a global difference of about 1.1 mag between the inner and outer parts of the galaxy. All the H II regions fall within the well-defined sequences of normal H II regions in the standard diagnostic diagrams [O III]/Hβ versus [N II]/Hα, and [O III]/Hβ versus [O I]/Hα. The values of excitation ([O III]/Hβ) of the regions located in the western arm are higher by about 0.4 dex compared to those of the eastern arm and central regions. There is evidence that the ionization parameter is higher and the electronic density lower in these regions. The global O/H abundance gradient is shallow (~-0.025±0.005 dex.kpc^–1), in agreement with what is found for galaxies with a strong bar. No break is seen in the O/H radial gradient. The azimuthal O/H variations in the disk are small at less than 0.3 dex. These results are discussed in the framework of a merger in which NGC 7479 captured a small galaxy about 3x10⁸ yr ago.