1210.8183 (M. A. Jimenez et al.)

The massive elliptical galaxy NGC 4649 from the perspective of extended gravity    [PDF]

M. A. Jimenez, G. Garcia, X. Hernandez

Elliptical galaxies are systems where dark matter is usually less necessary to explain observed dynamics than in the case of spiral galaxies, however there are some instances where Newtonian gravity and the observable mass are insufficient to explain their observed structure and kinematics. Such is the case of NGC 4649, a massive elliptical galaxy in the Virgo cluster for which recent studies report a high fraction of dark matter, 0.78 at $4R_e$. However this galaxy has been studied within the MOND hypothesis, where a good agreement with the observed values of velocity dispersion is found. In a similar way, we have constructed a self-consistent gravitational equilibrium dynamical model for this galaxy assuming a modified gravity force law, which is equivalent to MOND for $aa_{0}$. The modified gravity regime will be characterised by centrifugal equilibrium or dispersion velocities which become independent of distance, and which scale with the fourth root of the total baryonic mass, $V^{4}\propto(M G a_{0})$. We find that the recent detailed observations of the surface brightness profile and the velocity dispersion profile for this galaxy are consistent with the phenomenology expected in MONDian theories of modified gravity, without the need of invoking the presence of any hypothetical dark matter.

View original: http://arxiv.org/abs/1210.8183