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Caught in the act: cluster 'k+a' galaxies as a link between spirals and S0s

Caught in the act: cluster 'k+a' galaxies as a link between spirals and S0s Thumbnail


Bruno Rodriguez Del Pino

Steven P. Bamford


Bo Milvang-Jensen

Michael R. Merrifield

Marc Balcells


We use integral field spectroscopy of 13 disc galaxies in the cluster AC114 at z ∼ 0.31 in an attempt to disentangle the physical processes responsible for the transformation of spiral galaxies in clusters. Our sample is selected to display a dominant young stellar population, as indicated by strong Hδ absorption lines in their integrated spectra. Most of our galaxies lack the [O ii]λ3727 emission line, and hence ongoing star formation. They therefore possess ‘k+a’ spectra, indicative of a recent truncation of star formation, possibly preceded by a starburst. Discy ‘k+a’ galaxies are a promising candidate for the intermediate stage of the transformation from star-forming spiral galaxies to passive S0s. Our observations allow us to study the spatial distributions and the kinematics of the different stellar populations within the galaxies. We used three different indicators to evaluate the presence of a young population: the equivalent width of Hδ, the luminosity-weighted fraction of A stars, and the fraction of the galaxy light attributable to simple stellar populations with ages between 0.5 and 1.5 Gyr. We find a mixture of behaviours, but are able to show that in most of the galaxies the last episode of star formation occurred in an extended disc, similar to preceding generations of stars, though somewhat more centrally concentrated. We thus exclude nuclear starbursts and violent gravitational interactions as causes of the star formation truncation. Gentler mechanisms, such as ram-pressure stripping or weak galaxy–galaxy interactions, appear to be responsible for ending star formation in these intermediate-redshift cluster disc galaxies.


Rodriguez Del Pino, B., Bamford, S. P., Aragón-Salamanca, A., Milvang-Jensen, B., Merrifield, M. R., & Balcells, M. (2014). Caught in the act: cluster 'k+a' galaxies as a link between spirals and S0s. Monthly Notices of the Royal Astronomical Society, 438(2),

Journal Article Type Article
Acceptance Date Nov 11, 2013
Publication Date Feb 1, 2014
Deposit Date Apr 20, 2017
Publicly Available Date Apr 20, 2017
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 0035-8711
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 438
Issue 2
Keywords galaxies: clusters: individual: AC114, galaxies: evolution, galaxies: interactions
Public URL
Publisher URL
Additional Information This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society Published by Oxford University Press on behalf of the Royal Astronomical Society.


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