Formation and evolution of red Hdelta-strong galaxies in distant clusters: two different evolutionary paths to S0 galaxies?

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Title: Formation and evolution of red Hdelta-strong galaxies in distant clusters: two different evolutionary paths to S0 galaxies?
Author(s): Shioya, Yasuhiro; Bekki, Kenji; Couch, Warrick J.
Abstract: We numerically investigate the spectrophotometric evolution of galaxies with a variety of different star formation histories and degrees of dust extinction in order to elucidate the origin of the 'red Hδ-strong' (RHDS) galaxies - characterized by strong [EW(Hδ) > 3 Å] Balmer line absorption but with colors as red as the dormant E/S0 systems - first observed in distant clusters of galaxies. Specifically, we investigate the evolution in the [(B-R), EW(Hδ)]-plane of two different galaxy models: a 'truncation' model in which a galaxy with a declining star formation rate (typical of a normal spiral) has its star formation abruptly truncated, and a 'starburst' model in which a galaxy undergoes a secondary burst of star formation that is abruptly halted. This leads to the following three main results: (1) Both models pass through the zone inhabited by the RHDS galaxies in this plane, but the 'truncation' models cannot explain the most extreme cases, which have EW(Hδ) > 6 Å. (2) The reddest RHDS galaxies can only be explained by 'truncation' or 'starburst' models that have very heavy dust extinction (Av > 0.5 mag). (3) Irrespective of whether dust effects are included, the 'truncation' models are incapable of reproducing the very blue (B-R < 1.6) analogs of the RHDS galaxies. By comparing these results with recent Hubble Space Telescope-based morphological and ground-based spectroscopic studies of distant cluster galaxies, we propose that there are two possible different evolutionary paths for the transformation of cluster spirals into S0 galaxies.
Publication type: Journal article
Source: Astrophysical Journal, Vol. 601, no. 2 (Feb 2004), pp. 654-665
Publication year: 2004
FOR Code(s): 0201 Astronomical and Space Sciences
Keyword(s): Clusters; Galaxy formation; H delta; HST; Hubble Space Telescope; Interactions; ISM; Structure; RHDS
Publisher: University of Chicago Press
ISSN: 0004-637X
Publisher URL: http://dx.doi.org/10.1086/379817
Copyright: Copyright © 2004 The American Astronomical Society. All rights reserved. Publisher does not support archiving of either the postprint (final, revised accepted draft) or published version of full text in institutional repositories.
Peer reviewed