A Planck-selected dusty proto-cluster at z=2.16 associated with a strong over-density of massive H$\alpha$ emitting galaxies

TL;DR

This study identifies a dusty proto-cluster at z=2.16 with a significant over-density of H-alpha-emitting galaxies, revealing insights into galaxy clustering and star formation in the early universe.

Contribution

First detection of a Planck-selected dusty proto-cluster at z=2.16 with detailed H-alpha emitter analysis and clustering properties.

Findings

Massive H-alpha emitters are concentrated in the cluster core.

Most H-alpha emitters follow the star-forming main sequence.

Total star formation rate from H-alpha is lower than FIR estimates.

Abstract

We discovered an over-density of H-alpha-emitting galaxies associated with a Planck compact source in the COSMOS field (PHzG237.0+42.5) through narrow-band imaging observations with Subaru/MOIRCS. This Planck-selected dusty proto-cluster at z=2.16 has 38 H-alpha emitters including six spectroscopically confirmed galaxies in the observed MOIRCS 4'x7' field (corresponding to ~2.0x3.5~Mpc^2 in physical scale). We find that massive H-alpha emitters with log(M*/Msun)>10.5 are strongly clustered in the core of the proto-cluster (within ~300-kpc from the density peak of the H-alpha emitters). Most of the H-alpha emitters in this proto-cluster lie along the star-forming main sequence using H-alpha-based SFR estimates, whilst the cluster total SFR derived by integrating the H-alpha-based SFRs is an order of magnitude smaller than those estimated from Planck/Herschel FIR photometry. Our results suggest that H-alpha is a good observable for detecting moderately star-forming galaxies and tracing the large-scale environment in and around high-z dusty proto-clusters, but there is a possibility that a large fraction of star formation could be obscured by dust and undetected in H-alpha observations.