A spectroscopic study of a z=1.6 galaxy overdensity with GMASS

TL;DR

This study identifies and characterizes a galaxy overdensity at redshift 1.6, revealing its mass, galaxy composition, and stage of cluster formation through deep spectroscopic data.

Contribution

It provides the first detailed spectroscopic analysis of a galaxy overdensity at z=1.6, including mass, galaxy types, and formation history, indicating a cluster under assembly.

Findings

Overdensity factor of 11+/-3 at z=1.6

Velocity dispersion of 450 km/s

Total mass of ~7x10^14 solar masses

Abstract

The Galaxy Mass Assembly ultra-deep Spectroscopic Survey samples a part of the CDFS to unprecedented depth. The resulting distribution of 150 z>1.4 redshifts reveals a significant peak at z=1.6, part of a larger overdensity found at this redshift. The 42 spectroscopic members of this structure, called Cl 0332-2742, form an overdensity in redshift of a factor 11+/-3 and have a velocity dispersion of 450 km/s. We derive a total mass for Cl 0332-2742 of ~7x10^14 Msol. The colours of its early-type galaxies are consistent with a theoretical red sequence of galaxies with stars formed at z=3.0. In addition, there are more massive, passive and older, but less star forming galaxies in CL 0332-2742 than in the field. We conclude that this structure is a cluster under assembly at z=1.6.