EDP Sciences
Free access
Volume 464, Number 2, March III 2007
Page(s) 517 - 528
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20066446

A&A 464, 517-528 (2007)
DOI: 10.1051/0004-6361:20066446

Evolution of spiral galaxies in modified gravity

O. Tiret and F. Combes

Observatoire de Paris, LERMA, 61 Av. de l'Observatoire, 75014 Paris, France
    e-mail: olivier.tiret@obspm.fr

(Received 26 September 2006 / Accepted 4 December 2006)

We compare N-body simulations of isolated galaxies performed in both frameworks of modified Newtonian dynamics (MOND) and Newtonian gravity with dark matter (DM). We have developed a multigrid code able to efficiently solve the modified Poisson equation derived from the Lagrangian formalism AQUAL. We take particular care of the boundary conditions that are a crucial point in MOND. The 3-dimensional dynamics of initially identical stellar discs is studied in both models. In Newtonian gravity the live DM halo is chosen to fit the rotation curve of the MOND galaxy. For the same value of the Toomre parameter ($Q_{\rm T}$), galactic discs in MOND develop a bar instability sooner than in the DM model. In a second phase the MOND bars weaken while the DM bars continue to grow by exchanging angular momentum with the halo. The bar pattern speed evolves quite differently in the two models: there is no dynamical friction on the MOND bars so they keep a constant pattern speed while the DM bars slow down significantly. This affects the position of resonance like the corotation and the peanut. The peanut lobes in the DM model move radially outward while they keep the same position in MOND. Simulations of (only stellar) galaxies of different types on the Hubble sequence lead to a statistical bar frequency that is closer to observations for the MOND than the DM model.

Key words: galaxies: general -- galaxies: kinematics and dynamics -- galaxies: spiral -- galaxies: structure -- cosmology: dark matter

© ESO 2007