Journal Article

Weakening dark matter cusps by clumpy baryonic infall

David R. Cole, Walter Dehnen and Mark I. Wilkinson

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 416, issue 2, pages 1118-1134
Published in print September 2011 | ISSN: 0035-8711
Published online September 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19110.x
Weakening dark matter cusps by clumpy baryonic infall

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We consider the infall of a massive clump into a dark matter halo as a simple and extreme model for the effect of baryonic physics (neglected in gravity-only simulations of large-scale structure formation) on the dark matter. We find that such an infalling clump is extremely efficient in altering the structure of the halo and reducing its central density: a clump of 1 per cent the mass of the halo can remove about twice its own mass from the inner halo and transform a cusp into a core or weaker cusp. If the clump is subsequently removed, mimicking a galactic wind, the central halo density is further reduced and the mass removed from the inner halo doubled. Lighter clumps are even more efficient: the ratio of removed mass to clump mass increases slightly towards smaller clump masses. This process becomes more efficient the more radially anisotropic the initial dark matter velocities are. While such a clumpy infall may be somewhat unrealistic, it demonstrates that the baryons need to transfer only a small fraction of their initial energy to the dark matter via dynamical friction to explain the discrepancy between predicted dark matter density profiles and those inferred from observations of dark-matter-dominated galaxies.

Keywords: galaxies: formation; galaxies: haloes; galaxies: kinematics and dynamics; galaxies: structure

Journal Article.  13776 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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