ИСТИНА

Recent observational evidences in favour of `outside-in' lenticular galaxies evolution will be presented. In lenticular galaxies, large-scale stellar discs have appeared to be in average older than the bulges, and the bulges are older than the unresolved stellar nuclei. The discs are the oldest components of the lenticular galaxies: in our small sample of 20 nearby S0s, two thirds of all discs are older than 10 Gyr. It means that nearby S0s cannot be descendants of spiral galaxies falling into rich groups and clusters at the redshift of 0.4-0.5 (4-5 Gyr ago). I propose a new concept according to which S0s galaxies are primordial galaxy population forming at z>2 as thick clumpy discs. Later, at z<1, some primordial S0s transform into spirals by accreting outer cold gas and starting star formation in thin discs. In denser environments, in clusters and rich groups possessing X-ray emitting intracluster/intragroup medium, large reservoirs of cold gas cannot survive so the S0s in dense environments remain S0s up to the present epoch dominating there over other types of galaxies.