Various different physical processes contribute to the star formation and stellar mass assembly histories of galaxies .
One important approach to understand the significance of these different processes on galaxy evolution is the study of the stellar population content of today ’ s galaxies in a spatially resolved manner .
The aim of this paper is to characterize in detail the radial structure of stellar population properties of galaxies in the nearby universe , based on a uniquely large galaxy sample considering the quality and coverage of the data .
The sample under study was drawn from the CALIFA survey and contains 300 galaxies observed with integral field spectroscopy .
These cover a wide range of Hubble types , from spheroids to spiral galaxies , while stellar masses range from M _ { \star } \sim 10 ^ { 9 } to 7 \times 10 ^ { 11 } M _ { \odot } .
We apply the fossil record method based on spectral synthesis techniques to recover the following physical properties for each spatial resolution element in our target galaxies : the stellar mass surface density ( \mu _ { \star } ) , stellar extinction ( A _ { V } ) , light-weighted and mass-weighted ages ( \langle { log } age \rangle _ { L } , \langle { log } age \rangle _ { M } ) , and mass-weighted metallicity ( \langle { log } Z _ { \star } \rangle _ { M } ) .
To study mean trends with overall galaxy properties , the individual radial profiles are stacked in seven bins of galaxy morphology ( E , S0 , Sa , Sb , Sbc , Sc and Sd ) .
We confirm that more massive galaxies are more compact , older , more metal rich , and less reddened by dust .
Additionally , we find that these trends are preserved spatially with the radial distance to the nucleus .
Deviations from these relations appear correlated with Hubble type : earlier types are more compact , older , and more metal rich for a given M _ { \star } , which evidences that quenching is related to morphology , but not driven by mass .
Negative gradients of \langle { log } age \rangle _ { L } are consistent with an inside-out growth of galaxies , with the largest \langle { log } age \rangle _ { L } gradients in Sb–Sbc galaxies .
Further , the mean stellar ages of disks and bulges are correlated , with disks covering a wider range of ages , and late type spirals hosting younger disks .
However , age gradients are only mildly negative or flat beyond R \sim 2 HLR , indicating that star formation is more uniformly distributed or that stellar migration is important at these distances .
The gradients in stellar mass surface density depend mostly on stellar mass , in the sense that more massive galaxies are more centrally concentrated .
Whatever sets the concentration indices of galaxies obviously depends less on quenching / morphology than on the depth of the potential well .
There is a secondary correlation in the sense that at the same M _ { \star } early type galaxies have steeper gradients .
The \mu _ { \star } gradients outside 1 HLR show no dependence on Hubble type .
We find mildly negative \langle { log } Z _ { \star } \rangle _ { M } gradients , shallower than predicted from models of galaxy evolution in isolation .
In general , metallicity gradients depend on stellar mass , and less on morphology , hinting that metallicity is affected by the depth of both - potential well and morphology/quenching .
Thus , the largest \langle { log } Z _ { \star } \rangle _ { M } gradients occur in Milky Way-like Sb–Sbc galaxies , and are similar to those measured above the Galactic disk .
Sc spirals show flatter \langle { log } Z _ { \star } \rangle _ { M } gradients , possibly indicating a larger contribution from secular evolution in disks .
The galaxies from the sample have decreasing-outwards stellar extinction ; all spirals show similar radial profiles , independent from the stellar mass , but redder than E ’ s and S0 ’ s .
Overall we conclude that quenching processes act in manners that are independent of mass , while metallicity and galaxy structure are influenced by mass-dependent processes .