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Session 11 - Elliptical Galaxies.
Display session, Monday, June 10
Great Hall,

[11.05] Ionized Gas in Early-Type Galaxies: its effect on Mg\,b and other stellar line-strength indices

P. Goudfrooij (ESO), E. Emsellem (ESO)

In the light of the recent finding that nebular emission lines are commonly found in the inner regions of early-type galaxies, we evaluate their effect via stellar absorption-line indices. We derive analytical expressions for changes induced by the presence of nebular emission lines, both for atomic and molecular absorption-line indices. We find that the \sc [N\,i] emission-line doublet at 5199 Å\ can significantly affect Mg\,b line-strength measurements. For typical equivalent widths of the \sc [N\,i] doublet in nuclei of early-type galaxies featuring nebular emission, the Mg\,b index is artificially enhanced by 0.4\,--\,2 ÅThis represents a significant fraction of the typical equivalent width of the Mg\,b line in early-type galaxies. We argue that this effect should be considered when studying line-strength gradients in the inner regions of early-type galaxies. Several illustrations of this effect will be shown.

Program listing for Monday