The environmental impacts on the star formation main sequence: an H-alpha study of the newly discovered rich cluster at z=1.52

TL;DR

This study investigates how environment influences galaxy properties at z=1.52, revealing that passive galaxies dominate cluster cores while star-forming galaxies show less environmental dependence, indicating early environmental effects on galaxy evolution.

Contribution

It provides evidence that color and stellar mass-density relations are established at z~1.5 and explores the environmental dependence of the star formation main sequence at this epoch.

Findings

Passive red galaxies dominate cluster cores.

No significant SFR-density relation among star-forming galaxies.

Tentative evidence of starburst galaxies in small groups near the cluster.

Abstract

We report the discovery of a strong over-density of galaxies in the field of a radio galaxy at z=1.52 (4C65.22) based on our broad-band and narrow-band (H-alpha) photometry with Subaru Telescope. We find that H-alpha emitters are located in the outskirts of the density peak (cluster core) dominated by passive red-sequence galaxies. This resembles the situation in lower-redshift clusters, suggesting that the newly discovered structure is a well-evolved rich galaxy cluster at z=1.5. Our data suggest that the color-density and stellar mass-density relations are already in place at z~1.5, mostly driven by the passive red massive galaxies residing within Rc<200 kpc from the cluster core. These environmental trends almost disappear when we consider only star-forming (SF) galaxies. We do not find SFR-density or SSFR-density relations amongst SF galaxies, and the location of the SF main sequence does not significantly change with environment. Nevertheless, we find a tentative hint that star-bursting galaxies (up-scattered objects from the main sequence) are preferentially located in a small group at ~1-Mpc away from the main body of the cluster. We also argue that the scatter of the SF main sequence could be dependent on the distance to the nearest neighboring galaxy.