Eight luminous early-type galaxies in nearby pairs and sparse groups I.
  Stellar populations spatially analysed
  We present a detailed spatial analysis of stellar populations based on
long-slit optical spectra in a sample of eight luminous early-type galaxies
selected from nearby sparse groups and pairs, three of them may be interacting
with a galaxy of similar mass. We have measured luminosity-weighted averages of
age, [M/H], [Fe/H], and [$\alpha$/Fe] to add empirical data relative to the
influence of galaxy mass, environment, interaction, and AGN feedback in their
formation and evolution. The stellar population of the individual galaxies were
determined through the stellar population synthesis code STARLIGHT using
semi-empirical simple stellar population models. Radial variations of
luminosity-weighted means of age, [M/H], [Fe/H], and [$\alpha$/Fe] were
measured up to half of the effective radius of each galaxy. We found trends
between these values and the nuclear stellar velocity dispersion. There are
also relations between the metallicity/age gradients and the velocity
dispersion. Contributions of 1-4 Gyr old stellar populations were found in
IC5328 and NGC6758 as well as 4-8 Gyr old ones in NGC5812. Extended gas is
present in IC5328, NGC1052, NGC1209, and NGC6758, and the presence of a LINER
is identified in all these galaxies. The regions up to one effective radius of
all galaxies are dominated by $\alpha$-enhanced metal-rich old stellar
populations likely due to rapid star formation episodes that induced efficient
chemical enrichment. On average, the age and [$\alpha$/Fe] gradients are null
and the [M/H] gradients are negative, although discordant cases were found. We
found no correlation between the stellar population properties and the LINER
presence as well as between the stellar properties and environment or
gravitational interaction, suggesting that the influence of progenitor mass
can-not be discarded in the formation and evolution of early-type galaxies.
