The KMOS Cluster Survey (KCS) III: fundamental plane of cluster galaxies at $z \simeq 1.80$ in JKCS 041

TL;DR

This study constructs a fundamental plane for quiescent galaxies at redshift 1.80 in JKCS 041, revealing galaxy ages, structure, and potential merging activity, thus linking large-scale structure to galaxy evolution at high redshift.

Contribution

The paper presents the first fundamental plane analysis of galaxies at this redshift in JKCS 041, providing insights into galaxy formation and cluster assembly.

Findings

Derived galaxy formation redshift of z=3.0±0.3.

Identified age differences between galaxy groups within JKCS 041.

Suggested JKCS 041 may be in formation with merging groups.

Abstract

We present data for 16 galaxies in the overdensity JKCS 041 at $z \simeq 1.80$ as part of the K-band Multi-Object Spectrograph (KMOS) Cluster Survey (KCS). With 20-hour integrations, we have obtained deep absorption-line spectra from which we derived velocity dispersions for seven quiescent galaxies. We combined photometric parameters derived from Hubble Space Telescope images with the dispersions to construct a fundamental plane (FP) for quiescent galaxies in JKCS 041. From the zero-point evolution of the FP, we derived a formation redshift for the galaxies of $z_{form} = 3.0\pm0.3$, corresponding to a mean age of $1.4\pm0.2$ Gyrs. We tested the effect of structural and velocity dispersion evolution on our FP zero point and found a negligible contribution when using dynamical mass-normalized parameters ($\sim 3\%$), but a significant contribution from stellar-mass-normalized parameters ($\sim 42 \%$). From the relative velocities of the galaxies, we probed the three-dimensional structure of these 16 confirmed members of JKCS 041, and found that a group of galaxies in the south west of the overdensity had systematically higher velocities. We derived ages for the galaxies in the different groups from the FP. We found the east-extending group had typically older galaxies ($2.1\substack{+0.3\\-0.2}$ Gyrs), than those in the south-west group ($0.3\pm0.2$ Gyrs). Although based on small numbers, the overdensity dynamics, morphology, and age results could indicate that JKCS 041 is in formation and may comprise two merging groups of galaxies. The result could link large-scale structure to ages of galaxies for the first time at this redshift.