Astron. Astrophys. 332, 33-45 (1998)

The kinematically peculiar cores of the Coma cluster early-type galaxies NGC 4816 and IC 4051

D. Mehlert ^{* 1}, ^**, R.P. Saglia ¹, R. Bender ¹ and G. Wegner <sup>2

1</sup> Universitätssternwarte München, D-81679 München, Germany
² Department of Physics and Astronomy, 6127 Wilder Laboratory, Dartmouth College, Hanover, NH 03755-3528, USA

Received 24 July 1997 / Accepted 21 November 1997

Abstract

The Coma cluster is one of the richest known cluster of galaxies, spanning about 4 dex in density. Hence it is the ideal place to study the structure of galaxies as a function of environmental density in order to constrain the theories of galaxy formation and evolution. For a magnitude limited sample of 35 E and S0 galaxies we obtained long slit spectra to derive the rotation curves, the velocity dispersion profiles and the radial gradients of the Mg, Fe and H line indices. Here we report on two early - type galaxies which turned out to host the largest kinematically peculiar cores yet found in "normal" early - type galaxies: NGC 4816 hosts a decoupled counter rotating core with a radial extension along the major axis of 2.7 kpc, while IC 4051 has a co-rotating peculiar core with a sizes of 3.4 kpc. We combine our data with HST photometry and show that both cores are flattened central stellar disks which contribute less than 1 % to the total V band light of the galaxies, but are nevertheless conspicuous (1 - 2 10⁹ ). The metallicity of the cores is 0.25 dex super solar and drops to solar and sub solar in the outer part of NGC 4816 and IC 4051, respectively. The mean stellar population in both central disks is old (8 - 12 Gyr) and highly overabundant in relative to Fe (  0.5 dex). We discuss the evidence that these central disks formed via dissipational major merger events.

Key words: galaxies: elliptical and lenticular, cD kinematics and dynamics photometry abundances formations individual: NGC 4816 IC4051

* Visiting astronomer at the German-Spanish Astronomical Center, Calar Alto, operated by the Max-Planck-Institut für Astronomie, Heidelberg jointly with the Spanish National Commission for Astronomy.
** Visiting astronomer at the Michigan - Dartmouth - M.I.T. Observatory, Kitt Peak, Arizona, operated by a consortium of the University of Michigan, Dartmouth College and the Massachusetts Institute of Technology.

Send offprint requests to: D. Mehlert (mehlert@usm.uni-muenchen.de)

© European Southern Observatory (ESO) 1998

Online publication: March 10, 1998
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