X-ray Measurement of Dark Matter "Temperature" in Abell 1795

Details X-ray Measurement of Dark Matter "Temperature" in Abell 1795 X-ray Measurement of Dark Matter "Temperature" in Abell 1795

2004-02-26

arxiv.org/abs/astro-ph/0402634v2

Astrophys.J. 611 (2004) 175-185

Astronomy and Astrophysics

Astrophysics

ApJ in press

Scientific paper

10.1086/421986

We present a method from an X-ray observation of a galaxy cluster to measure the radial profile of the dark matter velocity dispersion, sigma_DM, and to compare the dark matter ``temperature'' defined as mu m_p sigma_DM**2 / k_B with the gas temperature. The method is applied to the XMM-Newton observation of Abell 1795. The ratio between the specific energy of the dark matter and that of the intracluster medium (ICM), which can be defined as beta_DM in analogy with beta_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 beta_DM value smaller than unity can most naturally be explained by heating of the ICM. The excess energy of ICM is estimated to be ~1-3 keV per particle.

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