We present estimates of stellar population ( SP ) gradients from stacked spectra of slow ( SR ) and fast ( FR ) rotator elliptical galaxies from the MaNGA-DR15 survey .
We find that : 1 ) FRs are \sim 5 Gyrs younger , more metal rich , less \alpha -enhanced and smaller than SRs of the same luminosity L _ { r } and central velocity dispersion \sigma _ { 0 } .
This explains why when one combines SRs and FRs , objects which are small for their L _ { r } and \sigma _ { 0 } tend to be younger .
Their SP gradients are also different .
2 ) Ignoring the FR/SR dichotomy leads one to conclude that compact galaxies are older than their larger counterparts of the same mass , even though almost the opposite is true for FRs and SRs individually .
3 ) SRs with \sigma _ { 0 } \leq 250 km s ^ { -1 } are remarkably homogeneous within \sim R _ { e } : they are old , \alpha -enhanced and only slightly super-solar in metallicity .
These SRs show no gradients in age and M _ { * } / L _ { r } , negative gradients in metallicity , and slightly positive gradients in [ \alpha /Fe ] ( the latter are model dependent ) .
SRs with \sigma _ { 0 } \geq 250 km s ^ { -1 } are slightly younger and more metal rich , contradicting previous work suggesting that age increases with \sigma _ { 0 } .
They also show larger M _ { * } / L _ { r } gradients .
4 ) Self-consistently accounting for M _ { * } / L gradients yields M _ { dyn } \approx M _ { * } because gradients reduce M _ { dyn } by \sim 0.2 dex while only slightly increasing the M _ { * } inferred using a Kroupa ( not Salpeter ) IMF .
5 ) The FR population all but disappears above M _ { * } \geq 3 \times 10 ^ { 11 } M _ { \odot } ; this is the same scale at which the size-mass correlation and other scaling relations change .
Our results support the finding that this is an important mass scale which correlates with the environment and above which mergers matter .