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We present deep echelle spectrophotometry of the Galactic HII region NGC2579. The data have been taken with the Very Large Telescope Ultraviolet-VisualEchelle Spectrograph in the 3550--10400 \AA\ range. This object, which has beenlargely neglected, shows however a rather high surface brightness, a highionization degree and is located at a galactocentric distance of 12.4 $\pm$ 0.7kpc. Therefore, NGC 2579 is an excellent probe for studying the behaviour ofthe gas phase radial abundance gradients in the outer disc of the Milky Way. Wederive the physical conditions of the nebula using several emissionline-intensity ratios as well as the abundances of several ionic species fromthe intensity of collisionally excited lines. We also determine the ionicabundances of C$^{2+}$, O$^+$ and O$^{2+}$ -- and therefore the total Oabundance -- from faint pure recombination lines. The results for NGC 2579permit to extend our previous determinations of the C, O and C/O gas phaseradial gradients of the inner Galactic disc (Esteban etal. 2005) to largergalactocentric distances. We find that the chemical composition of NGC 2579 isconsistent with flatten gradients at its galactocentric distance. In addition,we have built a tailored chemical evolution model that reproduces the observedradial abundance gradients of O, C and N and other observational constraints.We find that a levelling out of the star formation efficiency about and beyondthe isophotal radius can explain the flattening of chemical gradients observedin the outer Galactic disc.

NGC 2579 and the carbon and oxygen abundance gradients beyond the solar circle