Volume 488, Number 3, September IV 2008
|Page(s)||873 - 877|
|Published online||23 July 2008|
MOND vs. Newtonian dynamics in early-type galaxies
The case of NGC 4649 (M60)
Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia e-mail: [srdjan;mcirkovic]@aob.bg.ac.yu
Accepted: 12 June 2008
Context. Regarding the significant interest in both dark matter and the application of MOND to early-type galaxies, we investigate the MOND theory by comparing its predictions, for models of constant mass-to-light ratio, with observational data of the early-type galaxy NGC 4649.
Aims. We study whether measurements for NGC 3379 and NGC 1399 are typical of early-type systems and we test the assumption of a Newtonian constant M/L ratio underlying most of the published models.
Methods. We employ the globular clusters of NGC 4649 as a mass tracer. The Jeans equation is calculated for both MOND and constant mass-to-light ratio assumptions. Spherical symmetry is assumed and the calculations are performed for both isotropic and anisotropic cases.
Results. We found that both Jeans models with the assumption of a constant mass-to-light ratio and different MOND models provide good agreement with the observed values of the velocity dispersion. The most accurate fits of the velocity dispersion were obtained for the mass-to-light ratio in the B-band, which was equal to 7, implying that there is no need for significant amounts of dark matter in the outer parts (beyond 3 effective radii) of this galaxy. We also found that tangential anisotropies are most likely present in NGC 4649.
Key words: gravitation / galaxies: elliptical and lenticular, cD / galaxies: kinematics and dynamics / galaxies: halos / galaxies: individual: NGC 4649
© ESO, 2008
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