SDSS-IV MaNGA: Global stellar population and gradients for about 2000
  early-type and spiral galaxies on the mass-size plane
  We perform full spectrum fitting stellar population analysis and Jeans
Anisotropic modelling (JAM) of the stellar kinematics for about 2000 early-type
galaxies (ETGs) and spiral galaxies from the MaNGA DR14 sample. Galaxies with
different morphologies are found to be located on a remarkably tight mass plane
which is close to the prediction of the virial theorem, extending previous
results for ETGs. By examining an inclined projection (`the mass-size' plane),
we find that spiral and early-type galaxies occupy different regions on the
plane, and their stellar population properties (i.e. age, metallicity and
stellar mass-to-light ratio) vary systematically along roughly the direction of
velocity dispersion, which is a proxy for the bulge fraction. Galaxies with
higher velocity dispersions have typically older ages, larger stellar
mass-to-light ratios and are more metal rich, which indicates that galaxies
increase their bulge fractions as their stellar populations age and become
enriched chemically. The age and stellar mass-to-light ratio gradients for
low-mass galaxies in our sample tend to be positive ($\rm centre<outer$), while
the gradients for most massive galaxies are negative. The metallicity gradients
show a clear peak around velocity dispersion $\log_{10} \sigma_{\rm e}\approx
2.0$, which corresponds to the critical mass $\sim 3\times 10^{10}M_{\odot}$ of
the break in the mass-size relation. Spiral galaxies with large mass and size
have the steepest gradients, while the most massive ETGs, especially above the
critical mass $M_{\rm crit}\ge 2\times 10^{11} M_{\odot}$, where slow rotator
ETGs start dominating, have much flatter gradients. This may be due to
differences in their evolution histories, e.g. mergers.
