Insights into formation scenarios of massive Early-Type galaxies from
  spatially resolved stellar population analysis in CALIFA
  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
$\lesssim 2R_e$, as a function of radius and stellar-mass surface density
$\mu_*$. We study in detail the dependence of profiles on galaxies' global
properties, including velocity dispersion $\sigma_e$, stellar mass, morphology.
ETGs are universally characterized by strong, negative metallicity gradients
($\sim -0.3\,\text{dex}$ per $R_e$) within $1\,R_e$, which flatten out moving
towards larger radii. A quasi-universal local $\mu_*$-metallicity relation
emerges, which displays a residual systematic dependence on $\sigma_e$, whereby
higher $\sigma_e$ implies higher metallicity at fixed $\mu_*$. Age profiles are
typically U-shaped, with minimum around $0.4\,R_e$, asymptotic increase to
maximum ages beyond $\sim 1.5\,R_e$, and an increase towards the centre. The
depth of the minimum and the central increase anti-correlate with $\sigma_e$. A
possible qualitative interpretation of these observations is a two-phase
scenario. In the first phase, dissipative collapse occurs in the inner
$1\,R_e$, 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.
