Feeding the Beasts: Shedding light on the formation processes of today's most massive galaxies.

我们发现了宇宙中最大质量星系的一种新的--意想不到的--形成机制：最亮星系团或BCG。这些系统位于丰富而巨大的星系团的中心，通过其组成部分的相互引力而聚集在一起。尽管公认的标准理论表明，BCG应该通过较小的贫气系统(所谓的层次结构形成情景)的积累来聚集大部分恒星质量，但我的团队最近的结果表明，年轻的BCG发生了大量的原位恒星形成。这是一个关键的结果，因为作为进化的极端结果，这些大质量系统是星系形成模型的敏感探测器。这也令人惊讶，因为它与我们对星系团如何共生星系的理解背道而驰：在坠入星系团期间，星系应该被剥离其星际介质，当它们与BCG合并时，它们是贫气的-从而使恒星不可能形成。然而，BCGs内部和周围大量的恒星形成表明，大量的燃料已经沉积到这些星系团的中心。在接下来的五年里，我的团队将进行一项雄心勃勃的观测计划，以阐明这些系统中气体沉积和恒星形成的性质。具体地说，我们的目标是了解是什么触发了我们测量到的激烈的恒星形成，是什么维持了它，以及什么最终会使它熄灭。这将需要一种跨越光的电磁光谱的方法，因为不同的过程发射不同波长的光。我们将使用新的在线和下一代设施，如阿塔卡马大毫米阵列和詹姆斯·韦伯太空望远镜，以及老牌的主力设备，如双子座8M光学望远镜和詹斯基超大型(无线电)阵列。该计划将包括星系恒星质量组装的三个主要方面：(I)当前或正在进行的恒星形成；(Ii)现有恒星，或历史上的恒星形成；(Iii)分子气体燃料，或未来的恒星形成。这种三管齐下的方法将首次阐明这些大质量野兽的形成机制，并为形成我们理解大质量星系演化基础的模型和理论提供新的约束。

We have discovered a new - an unexpected - formation mechanism for the most massive galaxies in the universe: Brightest Cluster Galaxies or BCGs.  These systems sit at the centre of rich and massive galaxy clusters, held together by the mutual gravity of their components. Although the standard accepted theory indicates that BCGs should assemble the bulk of their stellar mass through the accretion of smaller gas-poor systems (the so-called hierarchical structure formation scenario) the recent results of my team have shown that substantial in-situ star formation occurs in young BCGs. This is a key result since, as an extreme outcome of evolution, these massive systems are sensitive probes of the models of galaxy formation. It is also surprising as it flies in the face of our understanding of how galaxy clusters accrete galaxies:  during in-fall into the cluster the galaxies should be stripped of their interstellar medium and be gas poor by the time they merge wit the BCG - thus making star formation impossible. Yet the immense amount of star formation in and around BCGs indicate that large amounts of fuel have been deposited into the centres of these galaxy clusters.  Over the next five years, my team will undertake an ambitious observational program to elucidate the nature of the gas deposition and star formation in these systems.  Specifically, our objective is to understand what triggered the intense star formation we have measured, what sustains it and what will eventually quench it.   This will require an approach the spans the electromagnetic spectrum of light as different processes emit light at different wavelengths. We will employ the newly-online and next generation facilities such as the Atacama Large Millimetre Array and the James Webb Space telescope, as well as established workhorses such as the Gemini 8m optical telescopes and the Jansky Very Large (radio) Array.    The program will encompass the three main aspects of galaxy stellar mass assembly:  (i) the current or ongoing star formation; (ii) the existing stars, or the historical star formation and; (iii) the molecular gas fuel, or the future star formation.  This three-pronged approach will clarify for the first time, the formation mechanisms of these massive beasts and provide new constraints for the models and theory which form the basis of our understanding of massive galaxy evolution.