Spatially resolved spectroscopy of the E+A galaxies in the z = 0.32 cluster AC 114

Author(s)

Pracy, Michael B.; Couch, Warrick J.; Blake, Chris; Bekki, Kenji; Harrison, Craig; Colless, Matthew; Kuntschner, Harald; De Propris, Roberto

Available versions

Abstract

We present spatially resolved intermediate-resolution spectroscopy of a sample of 12 E+A galaxies in the z= 0.32 rich galaxy cluster AC 114, obtained with the FLAMES multi-integral field unit system on the Very Large Telescope (VLT) of the European Southern Observatory. Previous integrated spectroscopy of all these galaxies by Couch & Sharples had shown them to have strong Balmer line absorption and an absence of [O ii]λ3727 emission – the defining characteristics of the 'E+A' spectral signature, indicative of an abrupt halt to a recent episode of quite vigorous star formation. We have used our spectral data to determine the radial variation in the strength of Hδ absorption in these galaxies and hence map out the distribution of this recently formed stellar population. Such information provides important clues as to what physical event might have been responsible for this quite dramatic change in star formation activity in the recent past of these galaxies. We find a diversity of behaviour amongst these galaxies in terms of the radial variation in Hδ absorption: four galaxies show little Hδ absorption across their entire extent; it would appear they were misidentified as E+A galaxies in the earlier integrated spectroscopic studies. The remainder show strong Hδ absorption, with a gradient that is either negative (Hδ equivalent width decreasing with radius), flat or positive. By comparison with numerical simulations we suggest that the first of these different types of radial behaviour provides evidence for a merger/interaction origin, whereas the latter two types of behaviour are more consistent with the truncation of star formation in normal disc galaxies with the Hδ gradient becoming increasingly positive with time after truncation. It would seem therefore that more than one physical mechanism is responsible for E+A formation in the same environment.

Publication year

2005

Publication type

Journal article

Source

Monthly Notices of the Royal Astronomical Society, Vol. 359, no. 4 (Jun 2005), pp. 1421-1432

ISSN

0035-8711

Publisher

Wiley

Copyright

Copyright © 2005 Royal Astronomical Society. The accepted manuscript is reproduced in accordance with the copyright policy of the publisher. The definitive publication is available at www.interscience.wiley.com.

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