从冷核到非冷核的来回：来自射电晕的线索
Back and forth from cool core to non-cool core: clues from radio-halos
摘要：
X射线天文学家通常将星系团分为两类：“冷核”（CC）和“非冷核”（NCC）天体。这种二分法的起源近年来一直是争论的主题，在“进化”模型（其中集群可以从CC发展到NCC，主要是通过合并）和“原始”模型（其中集群的状态是固定的“从头算”通过早期合并或预热）之间。我们发现，在一个定义明确的样本中（具有可用钱德拉或XMM-牛顿数据的GMRT射电晕调查中的集群），没有一个拥有巨大射电晕的物体可以被归类为冷核。这一结果表明，可以启动大规模同步辐射（最有可能合并）的主要机制是相同的，可以摧毁CC，因此强烈支持“进化”模型的CC-NCC二分法。此外，结合在CC和NCC状态的对象的数量与对象的数量有和没有无线电晕，我们估计，NCC集群松弛到CC状态的时间尺度，应该大于典型的无线电晕的寿命，可能短于约3 Gyr。这表明NCC转变成CC比从冷却时间预测的更快，在NCC系统中冷却时间约为10 Gyr，这允许CC和NCC状态之间的周期性演变的可能性。
英文摘要：
X-ray astronomers often divide galaxy clusters into two classes: "cool core" (CC) and "non-cool core" (NCC) objects. The origin of this dichotomy has been the subject of debate in recent years, between "evolutionary" models (where clusters can evolve from CC to NCC, mainly through mergers) and "primordial" models (where the state of the cluster is fixed "ab initio" by early mergers or pre-heating). We found that in a well-defined sample (clusters in the GMRT Radio halo survey with available Chandra or XMM-Newton data), none of the objects hosting a giant radio halo can be classified as a cool core. This result suggests that the main mechanisms which can start a large scale synchrotron emission (most likely mergers) are the same that can destroy CC and therefore strongly supports "evolutionary" models of the CC-NCC dichotomy. Moreover combining the number of objects in the CC and NCC state with the number of objects with and without a radio-halo, we estimated that the time scale over which a NCC cluster relaxes to the CC state, should be larger than the typical life-time of radio-halos and likely shorter than about 3 Gyr. This suggests that NCC transform into CC more rapidly than predicted from the cooling time, which is about 10 Gyr in NCC systems, allowing the possibility of a cyclical evolution between the CC and NCC states.
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