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arXiv · 1603.04437

The Ubiquity of Coeval Starbursts in Massive Galaxy Cluster Progenitors

Caitlin M. Casey
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Abstract

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 $2 10^{15} M_\odot$ 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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Caitlin M. Casey. 2016-03-14. The Ubiquity of Coeval Starbursts in Massive Galaxy Cluster Progenitors. https://doi.org/10.3847/0004-637x/824/1/36

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