Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics

Thermal Conduction, Feedback and Multiphase Gas in Galaxy
Clusters
Baban Wagh, Prateek Sharma
Galaxy clusters are the largest gravitationally bound, relaxed astronomical objects in the universe, with total
mass around 10 14 − 10 15 M ⊙ , where M ⊙ is a solar mass. Most of the cluster mass, about 85%, is in the dark
matter halo, while 15% is the baryonic mass. Of this 15%, around 90% is in the form of hot, X-ray emitting
plasma (∼ 10 7 − 10 8 K), called the intracluster medium (ICM). Due large gas density in the central regions,
the ICM loses energy primarily by bremsstrahlung radiation, and cools. But there is a discrepancy between
the predicted and the observed cooling rate in galaxy clusters, and this is called the cooling flow problem. It is
believed that the heat lost to cooling is replenished by feedback heating from the central supermassive black hole
and via thermal conduction bringing in heat from larger radii. Sharma and others ([1]) have identified ratio of
the thermal instability timescale and the free-fall time (t TI /t ff ) as an important factor in multiphase formation.
If t TI /t ff 10, then cold gas condenses from the hot phase from the ICM in thermal balance. Condensation
of cold gas is suppressed by thermal conduction, and thermal conduction in dilute ICM plasmas is along the
local magnetic field direction. We study the role of thermal conduction in multiphase gas formation in galaxy
clusters using idealized MHD simulations maintained in global thermal equilibrium. We find that while isotropic
conductivity can effectively suppress cold gas formation, anisotropic thermal conduction does not change the
t TI /t ff criterion based on hydro simulations. We also quantify the relative role of feedback heating and heating
due to thermal conduction in cluster cores.
References
[1] Sharma, P., McCourt, M., Quataert, E., & Parrish, I. J. 2012, MNRAS, 420, 3174
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