The variation of carbon abundance in galaxies and its implications

The trends of chemical abundances and abundance ratios observed in stars of different ages, kinematics, and metallicities bear the imprints of several physical processes which concur, thus shaping the host galaxy properties. By inspecting these trends, we obtain precious information on stellar nucleosynthesis, the stellar mass spectrum, the timescale of structure formation, the efficiency of star formation, as well as any inward or outward flows of gas. In this paper, we analyse recent determinations of carbon-to-iron and carbon-to-oxygen abundance ratios in different environments (the Milky Way and elliptical galaxies), using our latest chemical evolution models that implement up-to-date stellar yields and rely on the tight constraints provided by asteroseismic stellar ages, whenever available. A scenario where most carbon is produced by rotating massive stars, with yields largely dependent on the metallicity of the parent proto-star clouds, allowed us to simultaneously fit the high-quality data available for the local Galactic components (thick and thin discs) and for microlensed dwarf stars in the Galactic bulge, as well as the abundance ratios inferred for massive elliptical galaxies. Nevertheless, more efforts are needed from both observers and theoreticians in order to base these conclusions on firmer ground