Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-09-23
Astron.Astrophys.422:445-452,2004
Astronomy and Astrophysics
Astrophysics
Updated version to be published in Astronomy and Astrophysics. Original in "The Riddle of Cooling Flows in Galaxies and Cluste
Scientific paper
10.1051/0004-6361:20034415
We study the possibility that a large fraction of the gas at temperatures of \~10^7 K in cooling flow clusters cools by heat conduction to lower temperatures, rather than by radiative cooling. We argue that this process, when incorporated into the so-called "moderate cooling flow model", where the effective age of the intracluster medium is much lower than the age of the cluster, reduces substantially the expected X-ray luminosity from gas residing at temperatures of <10^7 K. In this model, the radiative mass cooling rate of gas at ~10^7 K inferred from X-ray observations, which is <20 % of the mass cooling rates cited in the past, is easily met. The heat conduction is regulated by reconnection between the magnetic field lines in cold (~10^4 K) clouds and the field lines in the intracluster medium. A narrow conduction front is formed, which, despite the relatively low temperature, allows efficient heat conduction from the hot ICM to the cold clouds. The reconnection between the field lines in cold clouds and those in the intracluster medium occurs only when the magnetic field in the ICM is strong enough. This occurs only in the very inner regions of cooling flow clusters, at r~10-30 kpc. The large ratio of the number of H\alpha photons to the number of cooling hydrogen atoms is explained by this scenario.
Blanton Elizabeth L.
Sarazin Craig L.
Soker Noam
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