标题： 大质量星系中[C II]、[O I]和CO的碰撞激发 显示英文标题

标题： Collisional excitation of [C II], [O I] and CO in Massive Galaxies

摘要： 在放松的星团和星系群的中心，许多大质量星系拥有巨大的低温（~10,000 K）和极冷（~100 K）气体储层。 在许多低红移最亮星系团和星系群中，这种气体被提升到炽热的星际介质（ISM）中，形成细丝状结构。这些细丝通常是长寿的，并且通常不会形成恒星。 两个重要的问题是：这些储层能冷却多远？如果存在丰富的冷气体，那么为何恒星形成效率如此之低？ 从周围X射线气体中的高温粒子碰撞和混合引起的加热和激发过程很好地描述了在细丝中观察到的光学和近红外发射线比值。 在本文中，我们研究了密集、寒冷云团的理论特性，这些云团通过发出[ C II ] 157 \mu 米、[ O I ] 63 \mu 米和CO的明亮谱线，暴露于这些高能电离粒子之下。 虽然某些发射线可能具有光学厚度，但我们发现这不足以建模发射线比值。 仅由热压力支持的细丝模型也不能解释冷气体的发射线比值，但来自湍流或磁场的非常适度的额外压力支持可以通过降低气体密度来拟合观测到的[ O I ]/[ C II ]发射线比值。 这可能还有助于稳定细丝以防止坍缩，从而导致较低的恒星形成率。 最后，我们预测了在这种条件下冷气体的预期发射线比值，并提供了用于与进一步观测比较的诊断图。 我们将代码作为附录提供。 显示英文摘要

摘要： Many massive galaxies at the centres of relaxed galaxy clusters and groups have vast reservoirs of cool (~10,000 K) and cold (~100 K) gas. In many low redshift brightest group and cluster galaxies this gas is lifted into the hot ISM in filamentary structures, which are long lived and are typically not forming stars. Two important questions are how far do these reservoirs cool and if cold gas is abundant what is the cause of the low star formation efficiency? Heating and excitation of the filaments from collisions and mixing of hot particles in the surrounding X-ray gas describes well the optical and near infra-red line ratios observed in the filaments. In this paper we examine the theoretical properties of dense, cold clouds emitting in the far infra-red and submillimeter through the bright lines of [C II]157 \mu m , [O I]63 \mu m and CO, exposed to these energetic ionising particles. While some emission lines may be optically thick we find this is not sufficient to model the emission line ratios. Models where the filaments are supported by thermal pressure support alone also cannot account for the cold gas line ratios but a very modest additional pressure support, either from turbulence or magnetic fields can fit the observed [O I]/[C II] line ratios by decreasing the density of the gas. This may also help stabilise the filaments against collapse leading to the low rates of star formation. Finally we make predictions for the line ratios expected from cold gas under these conditions and present diagnostic diagrams for comparison with further observations. We provide our code as an Appendix.