We present stellar population age and metallicity trends for a sample of 59 S0 galaxies based on optical SDSS and NIR J & H photometry .
When combined with optical g and r passband imaging data from the SDSS archive and stellar population models , we obtain radial age and metallicity trends out to at least 5 effective radii for most of the galaxies in our sample .
The sample covers a range in stellar mass and light concentration .
We find an average central light-weighted age of \sim 4 Gyr and central metallicity [ Z/H ] \sim 0.2 dex .
Almost all galaxies show a negative metallicity gradient from the center out , with an average value of \Delta [ Z/H ] / \Delta log ( r/ R _ { e } ) = -0.6 .
An age increase , decrease , and minimal change with radius is observed for 58 % , 19 % , and 23 % , respectively , for a mean age gradient of \Delta age / \Delta log ( r/R _ { e } ) = 2.3 Gyr dex ^ { -1 } .
For 14 out of 59 galaxies , the light-weighted age of the outer region is greater than 10 Gyr .
We find that galaxies with both lower mass and lower concentration have younger light-weighted ages and lower light-weighted metallicities .
This mass-metallicity relation extends into the outer regions of our S0 galaxies .
Our results are consistent with the formation of S0 galaxies through the transformation of spiral galaxy disks .
Determining the structural component that makes up the outer region of galaxies with old outksirts is a necessary step to understand the formation history of S0 galaxies .