The progeny of a Cosmic Titan: a massive multi-component proto-supercluster in formation at z=2.45 in VUDS

TL;DR

This paper uncovers a massive, complex proto-supercluster at z=2.45 using advanced 3D density mapping, revealing its structure, mass, and early collapse stages, providing new insights into supercluster formation.

Contribution

It introduces a novel 3D density field method combining spectroscopic and photometric redshifts to identify and analyze a large proto-supercluster at high redshift.

Findings

The proto-supercluster 'Hyperion' spans ~60x60x150 Mpc^3 with a mass of ~4.8x10^15 M_sun.

It contains at least 7 density peaks connected by filaments.

The peaks are predicted to virialize by z~0.8-1.6.

Abstract

[Abridged] We unveil the complex shape of a proto-supercluster at z~2.45 in the COSMOS field using the spectroscopic redshifts of the VIMOS Ultra-Deep Survey (VUDS), complemented by the zCOSMOS-Deep sample and high-quality photometric redshifts. The method relies on a 2D Voronoi tessellation in overlapping redshift slices that is converted into a 3D density field. The galaxy distribution is constructed using a statistical treatment of spectroscopic and photometric redshifts. We identify a proto-supercluster, dubbed "Hyperion" for its immense size and mass, which extends over a volume of ~60x60x150 comoving Mpc^3 and has an estimated total mass of ~4.8x 10^15 M_sun. This immensely complex structure contains at least 7 density peaks within 2.4 < z < 2.5, connected by filaments. Based on the peaks average matter density, we estimate their total mass, M_tot, and find a range of masses from ~0.1x10^14 M_sun to ~2.7x10^14 M_sun. By using spectroscopic members of each peak, we obtain the velocity dispersion of the galaxies in the peaks, and then their virial mass M_vir (under the strong assumption that they are virialised). The agreement between M_vir and M_tot is surprisingly good, considering that almost all the peaks are probably not yet virialised. According to the spherical collapse model, the peaks have already started or are about to start collapsing, and they are all predicted to be virialised by redshift z~0.8-1.6. We finally perform a careful comparison with the literature, given that smaller components of this proto-supercluster had previously been identified using heterogeneous galaxy samples. With VUDS, we obtain a panoramic view of this large structure, that encompasses, connects, and considerably expands in a homogeneous way on all previous detections of the various sub-components. This provides us the unique possibility to study a rich supercluster in formation.