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Gas-phase abundances in HII regions of two spiral galaxies, NGC7793 andNGC4945, have been studied to determine their radial metallicity gradients. Weused the strong-line method to derive oxygen abundances from spectra acquiredwith GMOS-S, the multi-object spectrograph on the 8m- Gemini South telescope.We found that NGC7793 has a well-defined gas-phase radial oxygen gradient of-0.321 $\pm$ 0.112 dex R$_{\rm 25}^{-1}$ (or -0.054 $\pm$ 0.019 dex kpc$^{-1}$)in the galactocentric range 0.17$<$R$_{\rm G}$/R$_{\rm 25}$ $<$ 0.82, notdissimilar from gradients calculated with direct abundance methods in galaxiesof similar mass and morphology. We also determined a shallow radial oxygengradient in NGC4945, -0.253 $\pm$ 0.149 dex R$_{\rm 25}^{-1}$ (or -0.019 $\pm$0.011 dex kpc$^{-1}$) for 0.04$<$R$_{\rm G}$/R$_{\rm 25}$ $<$ 0.51, where thelarger relative uncertainty derives mostly from the larger inclination of thisgalaxy. NGC7793 and NGC4945 have been selected for this study because they aresimilar, in mass and morphology, to M33 and the Milky Way, respectively. Sinceat zeroth order we expect the radial metallicity gradients to depend on massand galaxy type, we compared our galaxies in the framework of radialmetallicity models best suited for M33 and the Galaxy. We found a goodagreement between M33 and NGC7793, pointing toward similar evolution for thetwo galaxies. We notice instead differences between NGC4945 and the radialmetallicity gradient model that best fits the Milky Way. We found that thesedifferences are likely related to the presence of an AGN combined with a bar inthe central regions of NGC4945, and to its interacting environment.

Gas-phase oxygen abundances and radial metallicity gradients in the two nearby spiral galaxies NGC7793 and NGC4945