EDP Sciences
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Volume 396, Number 1, December II 2002
Page(s) 73 - 81
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20021333

A&A 396, 73-81 (2002)
DOI: 10.1051/0004-6361:20021333

A 60 pc counter-rotating core in NGC 4621

F. Wernli1, E. Emsellem1 and Y. Copin2

1  Centre de Recherche Astronomique de Lyon, 9 Av. Charles André, 69561 Saint-Genis Laval Cedex, France
2  Institut de physique nucléaire de Lyon, 4 rue Enrico Fermi, 69622 Villeurbanne Cedex, France

(Received 28 March 2002 / Accepted 10 September 2002)

We present adaptive optics assisted OASIS integral field spectrography of the S0 galaxy NGC 4621. Two-dimensional stellar kinematical maps (mean velocity and dispersion) reveal the presence of a ~ 60 pc diameter counter-rotating core (CRC), the smallest observed to date. The OASIS data also suggests that the kinematic center of the CRC is slightly offset from the center of the outer isophotes. This seems to be confirmed by archival HST/STIS data. We also present the HST/WFPC2 V-I colour map, which exhibits a central elongated red structure, also slightly off-centered in the same direction as the kinematic centre. We then construct an axisymmetric model of NGC 4621: the two-integral distribution function is derived using the Multi-Gaussian Expansion and the Hunter & Qian (1993) formalisms. Although the stellar velocities are reasonably fitted, including the region of the counter-rotating core, significant discrepancies between the model and the observations demonstrate the need for a more general model (e.g. a three-integral model).

Key words: galaxies: elliptical and lenticular, cD -- galaxies: evolution -- galaxies: individual: NGC 4621 -- galaxies: formation  -- galaxies: kinematics and dynamics -- galaxies: nuclei

Offprint request: F. Wernli, fabien@obs.univ-lyon1.fr

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