Effect of the large scale environment on the stellar content of early-typegalaxies

Tn order to study the influence of the environment on the stellar populatio n of early-type galaxies we have analyzed the relations between the density of the environment log(rho) and the residuals to the Mg-2 - sigma(0) relat ion, R-a, and between log(rho) and the residuals to the Fundamental Plane, RS. Our sample of galaxies covers the range of densities, between field gal axies and poor clusters. We confirm the existence of a slight environmental bias on the mean stellar population and we show that this effect is due to a small fraction of galaxies containing a younger stellar sub-population w hile the majority of galaxies, in any environment, are equally old. The gal axies which are likely to contain a young stellar sub-population (negative R-a and R-f) are preferentially found in the less dense environment. This segregation of the stellar population may reflect the morphology-densi ty relation or may result from a higher rate of recent star formation activ ity in sparse environments. Using the rotational support, V-max/sigma(0) to assess the presence of a disk and to parameterize the morphology, we subtr acted the contribution of the morphological segregation to population segre gation. It is not yet possible to rule out that the morphology-density rela tion is at the origin of the population-density relation.