A 100 Mpc$^2$ structure traced by hyperluminous galaxies around a massive $z$ = 2.85 protocluster

TL;DR

This study maps a large-scale structure at z=2.85 using submillimeter observations, revealing a massive, star-forming protocluster spanning 90 Mpc$^2$ with significant implications for understanding cluster formation.

Contribution

First wide-field submillimeter mapping of a z=2.85 protocluster, confirming its large scale and high star formation activity, linking observations with structure formation models.

Findings

SMGs span 90 Mpc$^2$ in the plane of the sky.

Total SFR from brightest galaxies is 20,000 M$_\ m\,yr^{-1}$.

Structure may evolve into a massive present-day galaxy cluster.

Abstract

We present wide-field mapping at 850 $\mu$m and 450 $\mu$m of the $z$ = 2.85 protocluster in the HS1549$+$19 field using the Submillimetre Common User Bolometer Array 2 (SCUBA-2). Spectroscopic follow-up of 18 bright sources selected at 850 $\mu$m, using the Nothern Extended Millimeter Array (NOEMA) and Atacama Large Millimeter Array (ALMA), confirms the majority lies near $z$ $\sim$ 2.85 and are likely members of the structure. Interpreting the spectroscopic redshifts as distance measurements, we find that the SMGs span 90 Mpc$^2$ in the plane of the sky and demarcate a 4100 Mpc$^3$ "pancake"-shaped structure in three dimensions. We find that the high star-formation rates (SFRs) of these SMGs result in a total SFR of 20,000 M$_\odot$ yr$^{-1}$ only from the brightest galaxies in the protocluster. These rapidly star-forming SMGs can be interpreted as massive galaxies growing rapidly at large cluster-centric distances before collapsing into a virialized structure. We find that the SMGs trace the Lyman-$\alpha$ surface density profile. Comparison with simulations suggests that HS1549$+$19 could be building a structure comparable to the most massive clusters in the present-day Universe.