The red sequence at birth in the galaxy cluster ClJ1449+0856 at z=2

TL;DR

This study investigates the early formation of the red sequence in a galaxy cluster at z=2, revealing a mix of galaxy types and transitional evolutionary stages in the cluster core, highlighting environmental effects at high redshift.

Contribution

It provides the first detailed analysis of the red galaxy population in a bona-fide cluster at z=2, showing early signs of red sequence development and environmental influence.

Findings

Red population includes quiescent and dusty star-forming galaxies.

A nascent red sequence is forming in the cluster core.

The color-magnitude diagram differs from lower-redshift clusters.

Abstract

We use HST/WFC3 imaging to study the red population in the IR-selected, X-ray detected, low-mass cluster Cl J1449+0856 at z=2, one of the few bona-fide established clusters discovered at this redshift, and likely a typical progenitor of an average massive cluster today. This study explores the presence and significance of an early red sequence in the core of this structure, investigating the nature of red sequence galaxies, highlighting environmental effects on cluster galaxy populations at high redshift, and at the same time underlining similarities and differences with other distant dense environments. Our results suggest that the red population in the core of Cl J1449+0856 is made of a mixture of quiescent and dusty star-forming galaxies, with a seedling of the future red sequence already growing in the very central cluster region, and already characterising the inner cluster core with respect to lower density environments. On the other hand, the color-magnitude diagram of this cluster is definitely different from that of lower-redshift (z<1) clusters, as well as of some rare particularly evolved massive clusters at similar redshift, and it is suggestive of a transition phase between active star formation and passive evolution occurring in the proto-cluster and established lower-redshift cluster regimes.