Martín-Navarro, IgnacioIgnacioMartín-NavarroVazdekis, AlexandreAlexandreVazdekisLA BARBERA, FrancescoFrancescoLA BARBERAFalcón-Barroso, JesúsJesúsFalcón-BarrosoLyubenova, MariyaMariyaLyubenovavan de Ven, GlennGlennvan de VenFerreras, IgnacioIgnacioFerrerasSánchez, S. F.S. F.SánchezTrager, S. C.S. C.TragerGarcía-Benito, R.R.García-BenitoMast, D.D.MastMendoza, M. A.M. A.MendozaSánchez-Blázquez, P.P.Sánchez-BlázquezGonzález Delgado, R.R.González DelgadoWalcher, C. J.C. J.WalcherCALIFA Team2020-06-232020-06-2320152041-8205http://hdl.handle.net/20.500.12386/26190We acknowledge support from grants AYA2013-48226-C3-1 P and AYA2010-15081 from the Spanish MINECO. C.J.W. acknowledges support through the Marie Curie Career Integration Grant 303912. P.S.-B. acknowledges support from the Ramón y Cajal program, ATA2010-21322-C03-02 (MINECO). J.F.B. and Gvd.V. acknowledge the DAGAL network from the People Programme (Marie Curie Actions) of the European Unions Seventh Framework Programme FP7/2007–2013 under REA grant agreement number PITN-GA-2011-289313.Variations in the stellar initial mass function (IMF) have been invoked to explain the spectroscopic and dynamical properties of early-type galaxies (ETGs). However, no observations have yet been able to disentangle the physical driver. We analyze here a sample of 24 ETGs drawn from the CALIFA survey, deriving in a homogeneous way their stellar population and kinematic properties. We find that the local IMF is tightly related to the local metallicity, becoming more bottom-heavy toward metal-rich populations. Our result, combined with the galaxy mass-metallicity relation, naturally explains previous claims of a galaxy mass-IMF relation, derived from non-IFU spectra. If we assume that—within the star formation environment of ETGs—metallicity is the main driver of IMF variations, a significant revision of the interpretation of galaxy evolution observables is necessary.STAMPAenArticle10.1088/2041-8205/806/2/L312-s2.0-84937570270000356772700010https://iopscience.iop.org/article/10.1088/2041-8205/806/2/L312015ApJ...806L..31MFIS/05 - ASTRONOMIA E ASTROFISICA