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Letter to the Editor
Effect of the large scale environment on the stellar content of early-type galaxies *
Ph. Prugniel 1,
V. Golev 1,2 and
G. Maubon 1
Received 25 March 1999 / Accepted 17 April 1999
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 and the residuals to the - relation, , and between and the residuals to the Fundamental Plane, . 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 galaxies 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 and ) 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.
Key words: galaxies: elliptical and lenticular, cD galaxies: formation galaxies: fundamental parameters galaxies: general galaxies: stellar content
Send offprint requests to: Ph. Prugniel (firstname.lastname@example.org
Online publication: May 21, 1999