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, metallicities, $\alpha$-element abundance ratios and
stellar initial mass functions) of early type galaxies (ETGs) at $z\le 0.08$
from the MaNGA-DR15 survey. In this work we focus on the S0 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 stellar
population synthesis models. This requires spectra with high signal-to-noise
which we achieve by stacking in bins of luminosity (L$_r$) and central velocity
dispersion ($\sigma_0$). We find that: 1) There is a bimodality in the S0
population: S0s more massive than $3\times 10^{10}M_\odot$ show stronger
velocity dispersion and age gradients (age and $\sigma_r$ decrease outwards)
but little or no metallicity gradient, while the less massive ones present
relatively flat age and velocity dispersion profiles, but a significant
metallicity gradient (i.e. [M/H] decreases outwards). Above
$2\times10^{11}M_\odot$ the number of S0s drops sharply. These two mass scales
are also where global scaling relations of ETGs change slope. 2) S0s have
steeper velocity dispersion profiles than fast rotating elliptical galaxies
(E-FRs) of the same luminosity and velocity dispersion. The kinematic profiles
and stellar population gradients of E-FRs are both more similar to those of
slow rotating ellipticals (E-SRs) than to S0s, suggesting that E-FRs are not
simply S0s viewed face-on. 3) At fixed $\sigma_0$, more luminous S0s and E-FRs
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.
