Environmental impact on star-forming galaxies in a $z \sim 0.9$ cluster during course of galaxy accretion

TL;DR

This study investigates how galaxy properties change during cluster assembly at z~0.9, revealing environmental effects like mergers, star formation enhancement, and quenching through detailed infrared and multi-wavelength observations.

Contribution

It provides new insights into galaxy evolution during cluster accretion at high redshift using narrow-band infrared imaging and phase-space analysis.

Findings

Identification of 27 Hα emitters associated with the cluster

Detection of galaxy groups likely in-falling into the cluster

Observation of increased star formation and mergers near the cluster

Abstract

Galaxies change their properties as they assemble into clusters. In order to understand the physics behind that, we need to go back in time and observe directly what is occurring in galaxies as they fall into a cluster. We have conducted a narrow-band and $J$-band imaging survey on a cluster CL1604-D at $z=0.923$ using a new infrared instrument SWIMS installed at the Subaru Telescope. The narrow-band filter, NB1261, matches to H$\alpha$ emission from the cluster at $z=0.923$. Combined with a wide range of existing data from various surveys, we have investigated galaxy properties in and around this cluster in great detail. We have identified 27 H$\alpha$ emitters associated with the cluster. They have significant overlap with MIPS 24$\mu$m sources and are located exclusively in the star forming regime on the rest-frame $UVJ$ diagram. We have identified two groups of galaxies near the cluster in the 2D spatial distribution and the phase-space diagram, which are likely to be in-falling to the cluster main body. We have compared various physical properties of star forming galaxies, such as specific star formation rates (burstiness) and morphologies (merger) as a function of environment; cluster center, older group, younger group, and the field. As a result, a global picture has emerged on how the galaxy properties are altered as they assemble into a denser region. This includes the occurrence of mergers, enhancement of star formation activity, excursion to the dusty starburst phase, and eventual quenching to a passive phase.