By undertaking deep long-slit spectroscopy with the focal reducer SCORPIO of the Russian 6m telescope , we studied stellar population properties and their variation with radius in 15 nearby S0 galaxies sampling a wide range of luminosities and environments .
For the large-scale stellar disks of S0s , we have measured SSP-equivalent metallicities ranging from the solar one down to [ Z/H ] = -0.4 - -0.7 , rather high magnesium-to-iron ratios , [ Mg/Fe ] \geq + 0.2 , and mostly old SSP-equivalent ages .
Nine of 15 ( 60 % \pm 13 % ) galaxies have large-scale stellar disks older than 10 Gyr , and among those we find all the galaxies which reside in denser environments .
The isolated galaxies may have intermediate-age stellar disks which are 7-9 Gyr old .
Only two galaxies of our sample , NGC 4111 and NGC 7332 , reveal SSP-equivalent ages of their disks of 2–3 Gyrs .
Just these two young disks appear to be thin , while the other , older disks have scale heights typical for thick stellar disks .
The stellar populations in the bulges at radii of 0.5 r _ { e } are on the contrary more metal-rich than the solar Z _ { \odot } , with the ages homogeneously distributed between 2 and 15 Gyr , being almost always younger than the disks .
We conclude that S0 galaxies could not form in groups at z \approx 0.4 as is thought now ; a new scenario of the general evolution of disk galaxies is proposed instead .