SIMBAD references

We perform spatially resolved stellar population analysis for a sample of 69 early-type galaxies (ETGs) from the CALIFA integral field spectroscopic survey, including 48 ellipticals and 21 S0's. We generate and quantitatively characterize profiles of light-weighted mean stellar age and metallicity within <=2Re, as a function of radius and stellar-mass surface density µ*. We study in detail the dependence of profiles on galaxies' global properties, including velocity dispersion σe, stellar mass, morphology. ETGs are universally characterized by strong, negative metallicity gradients ( -0.3 dex per Re) within 1Re, which flatten out moving towards larger radii. A quasi-universal local µ*-metallicity relation emerges, which displays a residual systematic dependence on σe, whereby higher σe implies higher metallicity at fixed µ*. Age profiles are typically U-shaped, with minimum around 0.4 Re, asymptotic increase to maximum ages beyond 1.5 Re, and an increase towards the centre. The depth of the minimum and the central increase anticorrelate with σe. A possible qualitative interpretation of these observations is a two-phase scenario. In the first phase, dissipative collapse occurs in the inner 1Re, establishing a negative metallicity gradient. The competition between the outside-in quenching due to feedback-driven winds and some form of inside-out quenching, possibly caused by central AGN feedback or dynamical heating, determines the U-shaped age profiles. In the second phase, the accretion of ex-situ stars from quenched and low-metallicity satellites shapes the flatter stellar population profiles in the outer regions.