Journal Article

Colour—magnitude relations and spectral line strengths in the Coma cluster

A. I. Terlevich, Harald Kuntschner, R. G. Bower, N. Caldwell and R. M. Sharples

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 310, issue 2, pages 445-452
Published in print December 1999 | ISSN: 0035-8711
Published online December 1999 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1046/j.1365-8711.1999.02941.x
Colour—magnitude relations and spectral line strengths in the Coma cluster

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We use the C24668, Fe4383, HγA and HδA spectral absorption line indices, together with U- and V-band photometry of 101 galaxies in the Coma cluster, to investigate how mean age and metal abundance correlate with galaxy luminosity. In particular, we use the line index measurements to address the origin of the colour—magnitude relation (CMR). We find that the CMR in Coma is driven primarily by a luminosity—metallicity correlation. We additionally show evidence for a relation between age and luminosity, in the direction predicted by the semi-analytic hierarchical clustering models of Kauffmann & Charlot, but this is only present in the C24668 index models, and could be an effect of the lack of non-solar abundance ratios in the Worthey models used.

By comparing deviations from the CMR with deviations in absorption index from analogous ‘index—magnitude’ relations, we find that colour deviations bluewards of the mean relation are strongly correlated with the hydrogen Balmer line series absorption. We show that the properties of these blue galaxies are consistent with the presence of a young stellar population in the galaxies, rather than with a reduced metallicity.

Keywords: galaxies: abundances; galaxies: clusters: individual: Coma; galaxies: elliptical and lenticular, cD; galaxies: formation; galaxies: starburst

Journal Article.  6019 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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