星系周围热气体的重新分布：冷云是否是解决过冷问题的信号？
Redistributing hot gas around galaxies: do cool clouds signal a solution to the overcooling problem?
摘要：
我们提出了一对高分辨率的光滑粒子流体动力学（SPH）模拟，探讨银河系大小的星系周围的热气体的演化和冷却行为。模拟包含相同的重子总质量和相同的初始气体密度分布的其他。第一个是初始化的低熵热气晕的曲线的暗物质，第二个是初始化的高熵热晕与核心的密度分布可能是预期的模型与预热反馈。星系形成的过程因初始设置的不同而有很大的不同。虽然低熵晕主要从中心区域迅速冷却，但高熵晕在~4 Gyr内是准稳定的，并最终通过~100 kpc距离的云的破碎和下沉而冷却。低熵晕的X射线表面亮度比目前的极限亮100倍，由此产生的盘状星系包含了系统中一半以上的重子。高熵晕的X射线亮度与观测结果一致，压力限制云的扩展分布让人想起观察到的人口，最后一个盘星系的质量是低熵模拟中形成的盘的一半，比角动量多50%。最后的高熵系统将其大部分重子保留在低密度的热晕中。热晕中有微量的冷的、大部分电离的、压力受限的云，在冷却10 Gyr后，这些云中含有约10%的重子。高熵晕中HI和MgII吸收云的覆盖率分别为~0.4和~0.6，尽管大部分为盘生长提供燃料的质量是电离的，因此在HI调查中会被低估。
英文摘要：
We present a pair of high-resolution smoothed particle hydrodynamics (SPH) simulations that explore the evolution and cooling behavior of hot gas around Milky-Way size galaxies. The simulations contain the same total baryonic mass and are identical other than their initial gas density distributions. The first is initialised with a low entropy hot gas halo that traces the cuspy profile of the dark matter, and the second is initialised with a high-entropy hot halo with a cored density profile as might be expected in models with pre-heating feedback. Galaxy formation proceeds in dramatically different fashion depending on the initial setup. While the low-entropy halo cools rapidly, primarily from the central region, the high-entropy halo is quasi-stable for ~4 Gyr and eventually cools via the fragmentation and infall of clouds from ~100 kpc distances. The low-entropy halo's X-ray surface brightness is ~100 times brighter than current limits and the resultant disc galaxy contains more than half of the system's baryons. The high-entropy halo has an X-ray brightness that is in line with observations, an extended distribution of pressure-confined clouds reminiscent of observed populations, and a final disc galaxy that has half the mass and ~50% more specific angular momentum than the disc formed in the low-entropy simulation. The final high-entropy system retains the majority of its baryons in a low-density hot halo. The hot halo harbours a trace population of cool, mostly ionised, pressure-confined clouds that contain ~10% of the halo's baryons after 10 Gyr of cooling. The covering fraction for HI and MgII absorption clouds in the high-entropy halo is ~0.4 and ~0.6, respectively, although most of the mass that fuels disc growth is ionised, and hence would be under counted in HI surveys.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
