Journal Article

Modelling ultrafine structure in dark matter haloes

Daniele S. M. Fantin, Michael R. Merrifield and Anne M. Green

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 390, issue 3, pages 1055-1060
Published in print November 2008 | ISSN: 0035-8711
Published online October 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13821.x
Modelling ultrafine structure in dark matter haloes

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Various laboratory-based experiments are underway attempting to detect dark matter directly. The event rates and detailed signals expected in these experiments depend on the dark matter phase-space distribution on submilliparsec scales. These scales are many orders of magnitude smaller than those that can be resolved by conventional N-body simulations, so one cannot hope to use such tools to investigate the effect of mergers in the history of the Milky Way on the detailed phase-space structure probed by the current experiments. In this paper, we present an alternative approach to investigate the results of such mergers, by studying a simplified model for a merger of a subhalo with a larger parent halo. With an appropriate choice of parent halo potential, the evolution of material from the subhalo can be expressed analytically in action-angle variables, so it is possible to obtain its entire orbit history very rapidly without numerical integration. Furthermore by evolving backwards in time, we can obtain arbitrarily high spatial resolution for the current velocity distribution at a fixed point. Although this model cannot provide a detailed quantitative comparison with the Milky Way, its properties are sufficiently generic that it offers qualitative insight into the expected structure arising from a merger at a resolution that cannot be approached with full numerical simulations. Preliminary results indicate that the velocity-space distribution of dark matter particles remains characterized by discrete and well-defined peaks over an extended period of time, both for single and multimerging systems, in contrast to the simple smooth velocity distributions sometimes assumed in predicting laboratory experiment detection rates. In principle, this structure contains a wealth of information about the formation history of the Milky Way's dark halo.

Keywords: methods: numerical; Galaxy: evolution; Galaxy: halo; Galaxy: kinematics and dynamics; solar neighbourhood; dark matter

Journal Article.  3400 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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