IMF-Metallicity: A tigh local relation revealed by the CALIFA survey

Astrophysical Journal Letters 806.2 (2015): L31 reproduced by permission of the AASVariations 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 necessaryWe 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-2011-28931