Journal Article

Galactic orbital motions in the dark matter, modified Newtonian dynamics and modified gravity scenarios

L. Iorio

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 401, issue 3, pages 2012-2020
Published in print January 2010 | ISSN: 0035-8711
Published online January 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.15811.x
Galactic orbital motions in the dark matter, modified Newtonian dynamics and modified gravity scenarios

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We simultaneously integrate in a numerical way the equations of motion of both the Magellanic Clouds (MCs) in the MOdified Newtonian Dynamics (MOND), MOdified Gravity (MOG) and cold dark matter (CDM) frameworks for −1 ≤t≤ 1 Gyr in order to see if, at least in principle, it is possible to discriminate between them. Since the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are at distances of approximately 50–60 kpc from the centre of the Milky Way (MW), they are ideal candidates for investigating the deep MOND regime occurring when the characteristic MOND acceleration A0= 1.2 × 10−10 m s−2 is larger than the internal acceleration A of the system considered; indeed, the Newtonian baryonic accelerations AN involved are about 0.02–0.03A0 for them. It turns out that CDM, MOND and MOG yield, in fact, different trajectories. In MOND the external field effect Aext must, in principle, also be considered. Since for the MW Aext≈ 0.01A0, with a lingering uncertainty, we consider both the cases Aext < AN, AextA0 and Aext=AN, AextA0. We also investigate the impact of the current uncertainties in the velocity components of MCs on their motions in the theories considered. In modelling the mutual interaction between the clouds and the dynamical friction (in CDM and MOND) we use for the masses of MCs the total (baryonic + dark matter) values, dynamically inferred, in CDM, and the smaller ones (baryonic), coming from direct detection of visible stars and neutral gas, in MOND and MOG.

Keywords: gravitation; methods: numerical; Galaxy: general; galaxies: kinematics and dynamics; Magellanic Clouds; dark matter

Journal Article.  6266 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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