Multi-Object Spectroscopy of Galaxy Clusters at $z \sim 0.95$ in Ultra Deep Survey Field with Different Star-formation Properties and Large-scale Environments

TL;DR

This study discovers two galaxy clusters at z~0.95 with similar masses but contrasting quiescent galaxy fractions, highlighting the influence of large-scale environments on galaxy quenching processes.

Contribution

It provides the first detailed spectroscopic analysis of two high-redshift clusters with contrasting star-formation properties in similar environments.

Findings

Clusters show contrasting quiescent galaxy fractions despite similar masses.

Large-scale environment correlates with quiescent galaxy fraction.

Replenishment of star-forming galaxies affects cluster quenching.

Abstract

While galaxy clusters are dominated by quiescent galaxies at local, they show a wide range in quiescent galaxy fraction (QF) at higher redshifts. Here, we present the discovery of two galaxy clusters at $z \sim 0.95$ with contrasting QFs despite having similar masses (log ($M_{200}/M_{\odot}$)$ \sim 14$) and spectra and redshifts of 29 galaxies in these clusters and 76 galaxies in the surrounding area. The clusters are found in the Ultra Deep Survey (UDS) field and confirmed through multi-object spectroscopic (MOS) observation using the Inamori Magellan Areal Camera and Spectrograph (IMACS) on the Magellan telescope. The two clusters exhibit QFs of $0.094^{+0.11}_{-0.032}$ and $0.38^{+0.14}_{-0.11}$, respectively. Analysis of large-scale structures (LSSs) surrounding these clusters finds that properties of these clusters are consistent with the anti-correlation trend between the QF and the extent of surrounding LSS, found in Lee et al. (2019), which can be interpreted as a result from the replenishment of young, star-forming galaxies keeps the QF low when galaxy clusters are accompanied by rich surrounding environments.