Initial Investigations of the Outskirts of XLSSC 122

TL;DR

This study explores the galaxy cluster XLSSC 122 at redshift 1.98 using HST data, analyzing galaxy distribution, color bimodality, and luminosity functions to understand galaxy evolution in the cluster outskirts.

Contribution

It provides an expanded catalog of member galaxies, analyzes their spatial and color distributions, and compares luminosity functions to lower redshift clusters, revealing insights into galaxy quenching and evolution.

Findings

No evidence of infalling groups or filaments in the outskirts.

Red galaxy fraction increases towards the cluster center.

Luminosity function similar to lower redshift clusters but with fainter scale magnitude.

Abstract

We investigate the redshift 1.98 galaxy cluster XLSSC 122 using the Hubble Space Telescope (HST) from the core of the cluster out to 3 Mpc, a scale equivalent to 10 times the R500 = 295 kpc radius. We present an expanded photometric and spectroscopic catalogue of the cluster, bringing the total number of spectroscopically classified member galaxies to 74, with 35 new member galaxies added in the outer regions of the cluster. We compute the radial galaxy number density profile in the cluster, and observe no clear evidence of infalling groups or cosmic filaments. We observe a clear bimodal colour relation in member galaxies, with red fraction increasing towards the cluster centre. This rapid increase of red fraction upon infall is indicative of a fast quenching mechanism, such as ram pressure stripping, as galaxies enter the cluster centre. We fit a luminosity function to the cluster members, finding a similar low mass slope but fainter scale magnitude than z = 1 clusters of similar temperature, implying a similar galaxy evolution rate to clusters at lower redshift.