Letter to the Editor

New light on the formation and evolution of bars^*

Trends in the stellar line-strength indices distribution inside the bar region

¹ Kapteyn Astronomical Institute, University of Groningen, The Netherlands e-mail: isa@astro.rug.nl
² Departamento de Física Teórica y del Cosmos, Universidad de Granada, Spain e-mail: azurita@ugr.es
³ Centre For Astrophysics, University of Central Lancashire, UK e-mail: psanchez-blazquez@uclan.ac.uk

Received: 6 December 2006
Accepted: 31 January 2007

Abstract

Aims.Our aim is to study the stellar content of the bar region to constrain its formation and evolution.

Methods.Line-strength indices in the bar region of a sample of 6 barred galaxies were employed to derive age and metallicity gradients along the bars using stellar population models.

Results.We find clear radial gradients in the line-strength indices for all the galaxies. We find positive gradients within the bar region in the metal indices in four of the six galaxies and opposite trends in the other two. These two galaxies are classified as SAB, and they present exponential bar light profiles. For all the galaxies, we find a positive gradient in the Balmer indices. There is a clear correlation between the position of morphological features inside the bar region with changes in the slope and value of the indices, which indicate changes in the stellar populations, when using stellar population analysis. Therefore, it seems that the bar regions show a gradient in both age and metallicity, changing radially to younger and more meta-rich populations for all the galaxies except for the two with exponential profiles.