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Main Authors: Todd, Eleanore. B., Willis, Jon. P., Canning, Rebecca. E. A., Leste, Ophélie. K., Alfarsy, Rahma., Allen, Steven W., Brammer, Gabriel, Burchett, Joseph. N., Mantz, Adam. B., Stanford, Spencer. A.
Format: Preprint
Published: 2026
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Online Access:https://arxiv.org/abs/2601.13492
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author Todd, Eleanore. B.
Willis, Jon. P.
Canning, Rebecca. E. A.
Leste, Ophélie. K.
Alfarsy, Rahma.
Allen, Steven W.
Brammer, Gabriel
Burchett, Joseph. N.
Mantz, Adam. B.
Stanford, Spencer. A.
author_facet Todd, Eleanore. B.
Willis, Jon. P.
Canning, Rebecca. E. A.
Leste, Ophélie. K.
Alfarsy, Rahma.
Allen, Steven W.
Brammer, Gabriel
Burchett, Joseph. N.
Mantz, Adam. B.
Stanford, Spencer. A.
contents 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.
format Preprint
id arxiv_https___arxiv_org_abs_2601_13492
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Initial Investigations of the Outskirts of XLSSC 122
Todd, Eleanore. B.
Willis, Jon. P.
Canning, Rebecca. E. A.
Leste, Ophélie. K.
Alfarsy, Rahma.
Allen, Steven W.
Brammer, Gabriel
Burchett, Joseph. N.
Mantz, Adam. B.
Stanford, Spencer. A.
Astrophysics of Galaxies
Cosmology and Nongalactic Astrophysics
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.
title Initial Investigations of the Outskirts of XLSSC 122
topic Astrophysics of Galaxies
Cosmology and Nongalactic Astrophysics
url https://arxiv.org/abs/2601.13492