A massive, distant proto-cluster at z=2.47 caught in a phase of rapid formation?

TL;DR

This study presents observations of a proto-cluster at z=2.47 with multiple starbursting galaxies and AGN, supporting rapid early cluster formation as predicted by hierarchical models.

Contribution

First observational evidence of a massive, filamentary proto-cluster at z=2.47 with multiple active galaxies, indicating rapid formation phases.

Findings

Contains seven starbursting, submillimeter-luminous galaxies and five AGN.

Cluster mass estimated to surpass that of the Coma supercluster at z~0.

Supports hierarchical growth models predicting rapid cluster assembly at high redshift.

Abstract

Numerical simulations of cosmological structure formation show that the Universe's most massive clusters, and the galaxies living in those clusters, assemble rapidly at early times (2.5 < z < 4). While more than twenty proto-clusters have been observed at z > 2 based on associations of 5-40 galaxies around rare sources, the observational evidence for rapid cluster formation is weak. Here we report observations of an asymmetric, filamentary structure at z = 2.47 containing seven starbursting, submillimeter-luminous galaxies and five additional AGN within a comoving volume of 15000 Mpc$^{3}$. As the expected lifetime of both the luminous AGN and starburst phase of a galaxy is ~100 Myr, we conclude that these sources were likely triggered in rapid succession by environmental factors, or, alternatively, the duration of these cosmologically rare phenomena is much longer than prior direct measurements suggest. The stellar mass already built up in the structure is $\sim10^{12}M_{\odot}$ and we estimate that the cluster mass will exceed that of the Coma supercluster at $z \sim 0$. The filamentary structure is in line with hierarchical growth simulations which predict that the peak of cluster activity occurs rapidly at z > 2.