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Date and Time of the Query: 2019-08-25 T22:31:08 PDT
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For refcode 1992A&A...258..250B:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1992A&A...258..250B Mg_2_ line-strength profiles of elliptical galaxies with kinematically decoupled cores R. Bender and P. Surma Landessternwarte Konigstuhl, W-6900 Heidelberg 1, Federal Republic of Germany Received October 22, 1991; accepted January 22, 1992 Abstract. A significant fraction of luminous ellipticals have been found to contain core components which are kinematically decoupled from their main bodies. This observation has been interpreted as a signature of violent merging processes in the formation of these galaxies. Here we show that the decoupling between central and outer parts of 4 presumed merger ellipticals also applies to their Mg_2_ profiles: in two of the four galaxies the Mg_2_ profile shows a significant change of slope at the same radius at which the peculiar core kinematics starts to become dominant. The other two galaxies show evidence for the same effect, but at a lower significance level. The decoupled core components exhibit high Mg_2_ line-strength indices and strong radial Mg_2_ gradients and are embedded in main bodies showing lower indices and weaker gradients. Attributing the gradients to changes in metallicity alone suggests that the decoupled core-components have metallicities about a factor 2 larger than those of the main bodies. Our findings may be understood in terms of either early hierarchical merging from objects quite different from present day galaxies (e.g. in the centers of clusters) or late merging of spirals (e.g. IRAS galaxies): while the stellar components of the progenitors violently relaxed and formed the main body of the merger remnant, a pre-enriched gas component efficiently lost angular momentum, settled in the central region and underwent a strong starburst phase. Because of the depth of the central potential the gas was well-confined, could be additionally enriched and formed a central stellar component with very high metallicities and peculiar kinematics. Kinematic peculiarities and decoupling are more likely to occur if the gas to star ratio was low in the progenitor objects. Key words: galaxies: elliptical - galaxies: formation of - galaxies: stellar content of
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