Effect of the large scale environment on the stellar content of early-type galaxies
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In order to study the influence of the environment on the stellar population of early-type galaxies we have analyzed the relations between the density of the environment (lrho) and the residuals to the Mg2-sigma relation, R_a, and between lrho and the residuals to the Fundamental Plane, R_f. Our sample of galaxies covers the range of densities, between field galaxies 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 galaxie s containing a younger stellar sub-population while the majority of galaxies, in any environment, are equally old. The galaxies 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-density relation or may result from a higher rate of recent star formation activity in sparse environments. Using the rotational support to assess the presence of a disk and to parameterize the morphology, we subtracted the contribution of the morphological segregation to population segregation. It is not yet possible to rule out that the morphology-density relation is at the origin of the population-density relation.
5 pages, 2 figures. Accepted for A&A (letters to the editors)
5 pages, 2 figures. Accepted for A&A (letters to the editors)