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Astron. Astrophys. 346, L25-L29 (1999)

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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

1 CRAL-Observatoire de Lyon (CNRS: UMR 142), F-69561 St-Genis-Laval Cedex, France
2 Department of Astronomy and Astronomical Observatory, University of Sofia, P.O. Box 36, BG-1504 Sofia, Bulgaria

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 [FORMULA] and the residuals to the [FORMULA] - [FORMULA] relation, [FORMULA], and between [FORMULA] and the residuals to the Fundamental Plane, [FORMULA]. 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 [FORMULA] and [FORMULA]) 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, [FORMULA], 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

* Based on observations collected at the Observatoire de Haute-Provence

Send offprint requests to: Ph. Prugniel (prugniel@galaxies.univ-lyon1.fr

© European Southern Observatory (ESO) 1999

Online publication: May 21, 1999