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

我们已经发现了一个新的——一个意想不到的——宇宙中最巨大星系的形成机制：最亮的星系团星系（bcg）。这些星系位于丰富而巨大的星系团的中心，由其组成部分的相互引力结合在一起。虽然公认的标准理论表明，BCGs应该通过较小的气体贫乏系统（所谓的分层结构形成情景）的吸积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BCGs中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，这些巨大的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吸积星系的理解背道而驰：在进入星系团的过程中，星系应该被剥夺了星际介质，并且在与BCG合并时缺乏气体——因此不可能形成恒星。然而，BCGs内部和周围的大量恒星形成表明，大量的燃料已经沉积在这些星系团的中心。

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.