Properties of Stellar Populations in Isolated Lenticular Galaxies
  In this paper we present the results of long-slit spectral observations for a
sample of isolated lenticular galaxies, made with the SCORPIO and SCORPIO-2
spectrographs of the 6-meter BTA telescope of the SAO RAS. By applying full
spectral fitting technique using the stellar population evolutionary synthesis
models, we have measured the radial profiles of the stellar line-of-sight
velocity as well as the velocity dispersion, SSP-equivalent age and
SSP-equivalent metallicity of stars along the radius in 12 targets. The
resulting averaged ages of the stellar population in bulges and discs cover an
entire range of possible values from 1.5 to 15 Gyr which indicates the absence
of a certain formation epoch for the structural components in the isolated
lenticular galaxies, unlike in the members of clusters and rich groups: they
could have been formed at a redshift of $z>2$ as well as only a few billion
years ago. Unlike S0 galaxies in more dense environments, the isolated galaxies
typically have the same age of stars in the bulges and discs. The disc-embedded
lenses and rings of increased stellar brightness, identified from the
photometry in 7 of 11 galaxies, do not differ strongly from the stellar discs
as concerning the properties of stellar populations and stellar velocity
dispersion. We conclude that the final shaping of the morphological type of a
lenticular galaxy in complete isolation is critically dependent on the possible
regimes of cold-gas accretion from outside.
