Witnessing pre-processing at intermediate redshift: observational evidence of infalling groups onto a merging galaxy cluster
Abstract
The fraction of quenched galaxies increases with local density, and part of this trend is thought to arise in groups before cluster accretion (pre-processing). In merging clusters, this is difficult to separate from star formation triggered or suppressed by the cluster merger itself. We investigate whether five high-velocity galaxies in the merging cluster SPT-CL~J0307-6225 (z=0.579), distributed in two candidate infalling groups, show signs of group-scale environmental processing prior to accretion. We combine MUSE integral-field spectroscopy and HST imaging to derive [\ion{O}{ii}] kinematic maps, spectral classes, and star-formation rates (SFR), to understand the properties of the galaxies. We further use the Magneticum simulations and the phase-space information to determine if these galaxies are part of two groups, and if they will be accreted onto the merging cluster. Group~1 is a morphologically disturbed interacting pair bound to the cluster, with at least one galaxy classified as dusty starburst. Group~2 is a compact triplet at ∼4σv from the cluster, in which two galaxies share a common [\ion{O}{ii}] envelope and the dominant member, an e(b) starburst, shows an elevated ionised-gas velocity dispersion. The SFR of both starburst galaxies lie within the scatter of the field star-forming main sequence, as expected for modest, interaction-triggered bursts. Close pairs at the phase-space position of group~2 occur for ∼1\% of comparable-mass cluster galaxies in Magneticum, so it is not unlikely for the group to be bound. Both groups show spatially resolved signatures of galaxy--galaxy interactions alongside ongoing star formation, supporting a pre-processing scenario in the environment of a merging cluster. Such group-scale interactions may contribute to the enhanced star formation reported in merging clusters.
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BibTeX
@misc{hernandezlang2026witnessing,
title = {{Witnessing pre-processing at intermediate redshift: observational evidence of infalling groups onto a merging galaxy cluster}},
author = {D. Hernández-Lang and D. Pallero and A. Ivleva and E. Sextl and N. Muñoz-Elgueta and J. Pierel and A. Zenteno and M. Bayliss and A. Calamida and E. R. Carrasco and G. Mahler and R. Monteiro-Oliveira and P. H. Prado and A. Rest and A. Saro},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.01344},
eprint = {2611.01344},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.01344},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Witnessing pre-processing at intermediate redshift: observational evidence of infalling groups onto a merging galaxy cluster
AU - D. Hernández-Lang
AU - D. Pallero
AU - A. Ivleva
AU - E. Sextl
AU - N. Muñoz-Elgueta
AU - J. Pierel
AU - A. Zenteno
AU - M. Bayliss
AU - A. Calamida
AU - E. R. Carrasco
AU - G. Mahler
AU - R. Monteiro-Oliveira
AU - P. H. Prado
AU - A. Rest
AU - A. Saro
PY - 2026
DA - 2026/11/01
PB - arXiv
DO - 10.48550/arxiv.2611.01344
UR - https://arxiv.org/abs/2611.01344
AB - The fraction of quenched galaxies increases with local density, and part of this trend is thought to arise in groups before cluster accretion (pre-processing). In merging clusters, this is difficult to separate from star formation triggered or suppressed by the cluster merger itself. We investigate whether five high-velocity galaxies in the merging cluster SPT-CL~J0307-6225 (z=0.579), distributed in two candidate infalling groups, show signs of group-scale environmental processing prior to accretion. We combine MUSE integral-field spectroscopy and HST imaging to derive [\ion{O}{ii}] kinematic maps, spectral classes, and star-formation rates (SFR), to understand the properties of the galaxies. We further use the Magneticum simulations and the phase-space information to determine if these galaxies are part of two groups, and if they will be accreted onto the merging cluster. Group~1 is a morphologically disturbed interacting pair bound to the cluster, with at least one galaxy classified as dusty starburst. Group~2 is a compact triplet at ∼4σ_v from the cluster, in which two galaxies share a common [\ion{O}{ii}] envelope and the dominant member, an e(b) starburst, shows an elevated ionised-gas velocity dispersion. The SFR of both starburst galaxies lie within the scatter of the field star-forming main sequence, as expected for modest, interaction-triggered bursts. Close pairs at the phase-space position of group~2 occur for ∼1\% of comparable-mass cluster galaxies in Magneticum, so it is not unlikely for the group to be bound. Both groups show spatially resolved signatures of galaxy--galaxy interactions alongside ongoing star formation, supporting a pre-processing scenario in the environment of a merging cluster. Such group-scale interactions may contribute to the enhanced star formation reported in merging clusters.
ER -