Galaxy properties as revealed by MaNGA III. Kinematic profiles and stellar population gradients in S0s

This is the third paper of a series where we study the stellar population gradients (SP; ages, rnetallicities, alpha-element abundance ratios, and stellar initial mass functions) of early-type galaxies (ETGs) at z <= 0.08 from the Mapping Nearby Galaxies at APO Data Release 15 (NlaNGA-DR,15) survey. In this work, we focus on the SO population and quantify how the SP varies across the population as well as with galactocentric distance. We do this by measuring Lick indices and comparing them to SP synthesis models, This requires spectra with high signal-to-noise ratio which we achiete by stacking in bins of luminosity (L-r) and central velocity dispersion (sigma(0)), We find that: (I) there is a bimodality in the SO population: SOs more massive than 3 x 10(10) M-circle dot show stronger velocity dispersion, and age gradients (age and sigma(r) decrease Outwards) but little or no rnetallicity gradient, while the less massive ones present relatively flat age and velocity dispersion profiles, but a significant metallicity gradient (i.e. [M/H1 decreases outwards). Above 2 x 10(11) M-circle dot, the number of SOs drops sharply. These two mass scales are also where global scaling relations of ETGs change slope. (2) SOs have steeper velocity: dispersion profiles than fast-rotating elliptical galaxies (E-FRs) of the same luminosity and velocity dispersion, The kinematic profiles and SP gradients of E-ERs are both more Sittliia to those of slow-rotating ellipticals (E-SRs) than to SOs, suggesting that E-ERs are not simply SOs viewed face-on. (3) At fixed cro, more luminous SOs and E-Fs are younger, more metal rich and less alpha-enhanced. Evidently for these galaxies, the usual statement that `massive galaxies are older' is not true if sigma(0) is held fixed.