Passive galaxies as tracers of cluster environments at z~2

TL;DR

This study uses passive galaxies as tracers to identify and analyze potential galaxy clusters at z~2, revealing overdensities that could represent early-stage clusters, thus offering insights into galaxy evolution and structure formation.

Contribution

It introduces a novel method of using passive galaxies to locate high-redshift galaxy clusters, expanding the tools for studying early universe structure formation.

Findings

Identified three strong passive galaxy overdensities at 1.5<z<2.5.

Proposed these overdensities as candidate galaxy clusters in early formation stages.

Demonstrated the potential of passive galaxies as tracers for high-redshift cluster environments.

Abstract

Even 10 billion years ago, the cores of the first galaxy clusters are often found to host a characteristic population of massive galaxies with already suppressed star formation. Here we search for distant cluster candidates at z~2 using massive passive galaxies as tracers. With a sample of ~40 spectroscopically confirmed passive galaxies at 1.3<z<2.1, we tune photometric redshifts of several thousands passive sources in the full 2 sq.deg. COSMOS field. This allows us to map their density in redshift slices, probing the large scale structure in the COSMOS field as traced by passive sources. We report here on the three strongest passive galaxy overdensities that we identify in the redshift range 1.5<z<2.5. While the actual nature of these concentrations is still to be confirmed, we discuss their identification procedure, and the arguments supporting them as candidate galaxy clusters (likely mid-10^13 M_sun range). Although this search approach is likely biased towards more evolved structures, it has the potential to select still rare, cluster-like environments close to their epoch of first appearance, enabling new investigations of the evolution of galaxies in the context of structure growth.