团内介质的重力热力学：负的heat capacity和冷却时标的膨胀
Gravo-thermodynamics of the Intracluster Medium: negative heat capacity and dilation of cooling time scales
摘要：
引力束缚的气态团内介质（ICM）冷却的时间尺度不仅仅由辐射过程决定。如果ICM在暗物质晕的固定引力场中处于准流体静力学平衡，那么由气体的引力势能引起的能量损失也应该考虑在内。这种“引力加热”已经知道了一段时间，使用显式解的运动方程。在这里，我们通过将维里定理应用于在外部引力场中处于准流体静力平衡的气体，忽略气体的引力，重新审视这种效应。对于一个标准的NFW形式的晕配置文件和有限的气体密度，气体温度的总能量的变化的响应显着延迟。在晕的尺度半径（$\rs$）内，有效冷却时间可以延长一个数量级以上。气体位于两倍于刻度半径的距离处，具有负热容，使得温度由于能量损失而升高。虽然外部加热（例如活动星系核活动）仍然需要解释缺乏冷ICM中心附近，这里的分析可能会规避加热的需要在更远的地区，有效的冷却时间可以延长，成为大于集群年龄，也解释了温度的增加，半径在这些地区。
英文摘要：
The time scale for cooling of the gravitationally bound gaseous intracluster medium (ICM) is not determined by radiative processes alone. If the ICM is in quasi-hydrostatic equilibrium in the fixed gravitational field of the dark matter halo then energy losses incurred by the gravitational potential energy of the gas should also be taken into account. This "gravitational heating" has been known for a while using explicit solutions to the equations of motion. Here, we re-visit this effect by applying the virial theorem to gas in quasi-hydrostatic equilibrium in an external gravitational field, neglecting the gravity of the gas. For a standard NFW form of halo profiles and for a finite gas density, the response of the gas temperature to changes in the total energy is significantly delayed. The effective cooling time could be prolonged by more than an order of magnitude inside the scale radius ($\rs$) of the halo. Gas lying at a distance twice the scale radius, has negative heat capacity so that the temperature increases as a result of energy losses. Although external heating (e.g. by AGN activity) is still required to explain the lack of cool ICM near the center, the analysis here may circumvent the need for heating in farther out regions where the effective cooling time could be prolonged to become larger than the cluster age and also explains the increase of temperature with radius in these regions.
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