2004/02/29 by Yasushi Ikebe, Y. Ikebe, Hans Boehringer +2
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Dark Matter and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1086/421986
published as Astrophys.J. 611 (2004) 175-185 · ApJ in press
arxiv created 2004/04/26 · openalex publication_date 2004/08/10 · arxiv updated 2009/12/01 · openalex created_date 2017/10/20 · openalex updated_date 2026/08/05
We present a method from an X-ray observation of a galaxy cluster to measure the radial profile of the dark matter velocity dispersion, σ DM , and to compare the dark matter "temperature" defined as μ m p σ / k B with the gas temperature. The method is applied to the XMM-Newton observation of A1795. The ratio between the specific energy of the dark matter and that of the intracluster medium (ICM), which can be defined as β DM in analogy with β spec , is found to be less than unity everywhere, ranging ~0.3-0.8. In other words, the ICM temperature is higher than the dark matter "temperature," even in the central region where the radiative cooling time is short. A β DM value smaller than unity can most naturally be explained by heating of the ICM. The excess energy of the ICM is estimated to be ~1-3 keV per particle.