ИСТИНА

By studying a large sample of 90 nearby S0 galaxies spread over a full range of luminosities and over different types of environment, with the IFU spectrograph MPFS installed at the Russian 6m telescope, we have measured mean stellar ages and abundances in their nuclei and in their bulges; the nuclei are in average 3~Gyr old, and the bulges are a few Gyr older. The subsequent long-slit study of the large-scale stellar disks in a smaller sample of S0s has revealed the older ages of the outer stellar disks with respect to the bulges. We conclude that the common paradigm of `inside-out' formation of disk galaxies is inapplicable to the S0s. Instead we propose a new scenario according to which the large-scale thick stellar disks are primordial components of S0 galaxies formed at z=1.5-2.5 from the highly turbulent thick gaseous disks observed at the high redshifts. The bulges of S0s had to rejuvenate and grow mostly at z<1 during the massive group and cluster assembling. Chemically distinct stellar nuclei are the products of more recent nuclear star formation bursts in the frame of this scenario.