Is the dark matter halo of the Milky Way flattened?

¹ Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401a, 141 31 Prague, Czech Republic e-mail: adam.ruzicka@gmail.com;palous@ig.cas.cz
² Faculty of Mathematics and Physics of the Charles University, Ke Karlovu 3, 121 16 Prague, Czech Republic
³ Institut für Astronomie der Universität Wien, Türkenschanzstrasse 17, 1180 Wien, Austria e-mail: theis@astro.univie.ac.at

Received: 3 May 2006
Accepted: 25 July 2006

Abstract

We performed an extended analysis of the parameter space for the interaction of the Magellanic System with the Milky Way (MW). The varied parameters cover the phase space parameters, the masses, the structure, and the orientation of both Magellanic Clouds, as well as the flattening of the dark matter halo of the MW. The analysis was done by a specially adopted optimization code searching for the best match between numerical models and the detailed H I map of the Magellanic System by Brüns et al. (2005, A&A, 432, 45). The applied search algorithm is a genetic algorithm combined with a code based on the fast, but approximative restricted N-body method. By this, we were able to analyze more than 10⁶ models, which makes this study one of the most extended ones for the Magellanic System. Here we focus on the flattening q of the axially symmetric MW dark matter halo potential, that is studied within the range . We show that creation of a trailing tail (Magellanic Stream) and a leading stream (Leading Arm) is quite a common feature of the Magellanic System-MW interaction, and such structures were modeled across the entire range of halo flattening values. However, important differences exist between the models, concerning density distribution and kinematics of H I, and also the dynamical evolution of the Magellanic System. Detailed analysis of the overall agreement between modeled and observed distribution of neutral hydrogen shows that the models assuming an oblate () dark matter halo of the Galaxy allow for better satisfaction of H I observations than models with other halo configurations.