大质量星系团祖先星暴的普遍性
The Ubiquity of Coeval Starbursts in Massive Galaxy Cluster Progenitors
摘要：
宇宙中最大的星系团很可能是在维里化之前，在同时发生的短暂的活动爆发中建造了大部分大质量的$>10^{11} M_\odot$星系。这一结论是从新兴的数据集上$z>2$原星系团和他们的成员星系的特点，特别是，罕见的星爆和超铝活动星系核（AGN）。在识别这类结构时，最具挑战性的观测障碍是它们非常大的体积，$\sim10^{4}$与Mpc $^3$在$z>2$同时运动，对着天空上半度的区域$\sim$。因此，与背景相比，非常稀有的星系过多所提供的对比度可以更容易地将过密结构与周围的正常密度场区分开来。详细讨论了文献中的五个$2<z<3$原星系团，发现每个原星系团包含多达12个尘埃星暴或发光活动星系核星系，这种现象即使在过密的环境中也不太可能偶然发生。对气体耗尽时间的测量表明，在$\sim$ 1亿年的时间尺度上，它们确实是短暂的，并且发现包含8个以上这样的系统的结构的概率是$\sim$ 0.2%，除非它们的“触发”在非常大的空间尺度上相关，$\sim$ 10 Mpc。富含恒星爆发的原星系团的体积密度被发现与附近宇宙中所有的$>10^{15} M_\odot$星系团相当，比某些模拟中预期的大五倍。在测量富含星爆的原星系团的体积密度和期望它们是通过短暂的插曲产生之间存在着一些紧张关系。然而，对大面积天空中原星系团的更好观测，肯定会对星系团的组装，以及它们是否通过这里所建议的偶发爆发来构建星系提供更多的线索。[删节]
英文摘要：
The Universe's largest galaxy clusters likely built the majority of their massive $>10^{11} M_\odot$ galaxies in simultaneous, short-lived bursts of activity well before virialization. This conclusion is reached from emerging datasets on $z>2$ proto-clusters and the characteristics of their member galaxies, in particular, rare starbursts and ultraluminous active galactic nuclei (AGN). The most challenging observational hurdle in identifying such structures is their very large volumes, $\sim10^{4}$ comoving Mpc$^3$ at $z>2$, subtending areas $\sim$half a degree on the sky. Thus the contrast afforded by an overabundance of very rare galaxies in comparison to the background can more easily distinguish overdense structures from the surrounding, normal density field. Five $2<z<3$ proto-clusters from the literature are discussed in detail and are found to contain up to 12 dusty starbursts or luminous AGN galaxies each, a phenomenon that is unlikely to occur by chance even in overdense environments. Measurements of gas depletion times suggest that they are indeed short-lived on $\sim$100 Myr timescales, and the probability of finding a structure containing more than 8 such systems is $\sim$0.2\%, unless their `triggering' is correlated on very large spatial scales, $\sim$10 Mpc across. The volume density of starburst-rich proto-clusters is found to be comparable to all $>10^{15} M_\odot$ galaxy clusters in the nearby Universe, a factor of five larger than expected in some simulations. Some tension yet exists between measurements of their volume density of starburst-rich proto-clusters and the expectation that they are generated via short-lived episodes. However, improved observations of proto-clusters over large regions of sky will certainly shed more light on the assembly of galaxy clusters, and whether or not they build their galaxies through episodic bursts as suggested here. [abridged]
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