Astronomy and Astrophysics – Astronomy
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006apj...642..140c&link_type=abstract
The Astrophysical Journal, Volume 642, Issue 1, pp. 140-151.
Astronomy and Astrophysics
Astronomy
24
Convection, Galaxies: Cooling Flows, Galaxies: Active, Galaxies: Clusters: General, Magnetic Fields, Turbulence
Scientific paper
Recent studies suggest that active galactic nuclei and cosmic rays drive convection in galaxy-cluster plasmas and that convection heats cluster cores and regulates the plasma temperature profile. In this paper, we investigate the convective stability of the intracluster medium. Previous work has described how magnetic fields modify the convective stability criterion by causing heat to diffuse primarily along magnetic field lines. We extend earlier analyses by including cosmic rays and cosmic-ray diffusion. We consider an equilibrium in which the gravitational acceleration is in the -ẑ-direction, the magnetic field is perpendicular to ẑ, and the magnetic pressure is much less than the thermal pressure. We use a local linear stability analysis to show that the convective stability criterion is nkBdT/dz+dpcr/dz>0, where n, T, and pcr are the plasma particle density, temperature, and cosmic-ray pressure, respectively. We also present approximate solutions to the dispersion relation and describe the different waves and instabilities present in the plasma. Because the stability criterion differs markedly from the Schwarzschild criterion, galaxy-cluster plasmas can be convective even though the specific entropy increases outward.
Chandran Benjamin D.
Dennis Timothy J.
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