Date and Time of the Query: 2019-06-20 T06:59:04 PDT
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For refcode 2005ApJ...620..191C:
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2005ApJ...620..191C A Two-Fluid Thermally Stable Cooling Flow Model Renyue Cen Abstract. A new model for cooling flows in X-ray clusters, capable of naturally explaining some salient features observed, is proposed. The only requirement is that a significant relativistic component, in the form of cosmic rays (CRs), be present in the intracluster medium and significantly frozen to the thermal gas. Such an addition qualitatively alters the conventional isobaric thermal instability criterion, such that a fluid parcel becomes thermally stable when its thermal pressure drops below a threshold fraction of its CR pressure. Consequently, the lowest possible temperature at any radius is about one-third of the ambient temperature, as observed, for X-ray clusters with temperatures greater than about 1.5 keV. An overall heating process is still required to balance the cooling lost to X-rays, but the temperature floor produced by this mechanism applies regardless of the nature of the heating process as long as the heating rate per unit mass is nearly independent of density. Completely separately, we suggest that dissipation of internal gravity waves, excited by radial oscillatory motions of inward-drifting cooling clouds about their radial equilibrium positions, may be responsible for heating up cooling gas. Because the ultimate energy source for powering the cooling X-ray luminosity and heating up cooling gas is gravitational, generated by inward-drifting cooling clouds as well as the general inward flow, heating is spatially distributed and energetically matched with cooling. One desirable property of this heating mechanism is that heating energy is strongly centrally concentrated, providing the required heating for emission-line nebulae. Keywords: Galaxies: Cooling Flows, ISM: Cosmic Rays, Galaxies: Clusters: General
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