Tuesday

We present how the C, N and O chemical abundances within the ISM of galaxies can be combined together to define genuine chemical diagnostics for the galaxy SFH. We make use of an hydrodynamical cosmological simulation and we focus our analysis on the redshift evolution of three star forming disc galaxies, characterised by different SFHs. We find that the log(C/N) ratios are highly sensitive to the past galaxy SFH and conclude that their evolution within galaxies is mostly regulated by the opposite metallicity dependence of the C and N stellar yields from the AGB stars; in particular, AGB stars with larger Z produce more N and less C and this fact amplifies the decrease of the log(C/N) ratios with time. The strong metallicity dependence of the C and N stellar yields from AGB stars explains also the predicted radial profile of the log(C/N) ratios at redshift z=0, along the galaxy disc.