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29 March 2024
 
  » arxiv » astro-ph/0309412

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Flat-Cored Dark Matter in Cuspy Clusters of Galaxies
Amr El-Zant ; Yehuda Hoffman ; Joel Primack ; Francoise Combes ; Isaac Shlosman ;
Date 15 Sep 2003
Journal Astrophys.J. 607 (2004) L75-L78
Subject astro-ph
AffiliationCaltech), Yehuda Hoffman (Hebrew Univ.), Joel Primack (UCSC), Francoise Combes (LERMA, Obs. de Paris), Isaac Shlosman (UK, Lexington
AbstractSand, Treu, & Ellis (2002) have measured the central density profile of cluster MS2137-23 with gravitational lensing and velocity dispersion and removed the stellar contribution with a reasonable M/L. The resulting dark matter distribution within r<50 kpc was fitted by a density cusp of r^{-beta} with beta=0.35. This stands in an apparent contradiction to the CDM prediction of beta~1, and the disagreement worsens if adiabatic compression of the dark matter by the infalling baryons is considered. Following El-Zant, Shlosman & Hoffman (2001), we argue that dynamical friction acting on galaxies moving within the dark matter background counters the effect of adiabatic compression by transfering the orbital energy of galaxies to the dark matter, thus heating up and softening the central density cusp. Using N-body simulations of massive solid clumps moving in clusters we show that indeed the inner dark matter distribution flattens (with beta approx 0.35 for a cluster like MS2137-23) when the galaxies spiral inward. We find as a robust result that while the dark matter distribution becomes core-like, the overall mass distribution preserves its cuspy nature, in agreement with X-ray and lensing observations of clusters.
Source arXiv, astro-ph/0309412
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