J/A+A/710/A57 redMaPPer clusters with ident. substructure (Tuomainen+, 2026)
Substructure in redMaPPer clusters and its impact on X-ray morphology and
scaling relations.
Tuomainen R., Finoguenov A., Comparat J., Doubrawa L.
<Astron. Astrophys. 710, A57 (2026)>
=2026A&A...710A..57T 2026A&A...710A..57T (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; X-ray sources ; Optical ; Redshifts
Keywords: dark matter - large-scale structure of the Universe -
X-rays: galaxies: clusters
Abstract:
Numerical simulations of hierarchical structure formation predict that
galaxy clusters retain significant dark matter substructure, a
signature of their ongoing assembly. This substructure is traced by
both the spatial distribution of member galaxies and perturbations in
the hot intracluster medium. Merging events significantly impact the
thermodynamic state of clusters, introducing scatter in observable
mass scaling relations and thereby affecting their use as precision
cosmology probes.
We statistically quantified the prevalence and properties of
substructure in optical galaxy clusters and directly investigated its
impact on X-ray morphology and scaling relations, leveraging new data
from the DECaLS Legacy Survey and the SRG/eROSITA all-sky survey.
We applied the hierarchical density-based clustering algorithm HDBSCAN
to the redMaPPer galaxy cluster catalog to identify and characterize
substructure from the probabilistic membership assignments. This
provides a refined membership catalog and a classification of each
cluster as containing substructure or not. We then cross-matched this
sample with the eROSITA X-ray morphology catalog to correlate optical
substructure with a comprehensive set of X-ray morphological
parameters. Finally, we analyzed the scaling relation between X-ray
luminosity and optical richness for clusters with and without
substructure.
Substructure is a common feature, present in approximately 40% of
clusters; a quarter of the full sample exhibits a fractional
contribution to richness in excess of 35%. We find a highly
significant correlation between optical substructure and disturbed
X-ray morphologies, a trend that is strongest for high-mass clusters.
The clusters with substructure also drive a stronger redshift
evolution in the scatter of the Lx-λ relation. At low redshifts
(z<0.2), they display a systematically higher X-ray luminosity at
fixed richness compared to relaxed systems.
We demonstrate that substructure identification with redMaPPer is
viable and essential for enhancing the precision of cluster cosmology.
We attribute the enhanced effect of mergers on X-ray properties at low
redshifts to the increased density contrast of low-redshift cool cores
and longer substructure survival times, which are possibly due to the
suppression of disruptive mixing by effects such as magnetic draping.
At lower cluster richness, a discordance between X-ray morphology and
the merging state indicates a growing relative importance of active
galactic nucleus feedback in governing X-ray morphology.
Description:
Tables provide details on the redMaPPer clusters with identified
substructure and eROSITA counterparts. X-ray properties are from
Bulbul et. al (2024A&A...685A.106B 2024A&A...685A.106B, Cat. J/A+A/685/A106).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
main.dat 244 2159 redMaPPer clusters with identified substructure
members.dat 108 121652 Cluster member galaxy catalogue
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See also:
J/A+A/685/A106 : eRASS. Galaxy clusters and groups in WGH (Bulbul+, 2024)
Byte-by-byte Description of file: main.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Name 1eRASS Name (IAUNAME)
25- 56 A32 --- DetUID eROSITA detection id
58- 72 F15.11 deg RAdeg X-ray cluster center right ascension (J2000)
74- 88 F15.11 deg DEdeg X-ray cluster center declination (J2000)
90- 95 F6.4 --- z1 Redshift of X-ray source
97-116 I20 --- Cluster Cluster id
118-132 F15.11 deg RA2deg Optical center right ascension (J2000)
134-148 F15.11 deg DE2deg Optical center declination (J2000)
150-157 F8.6 --- z2 Redshift of optical cluster
159 I1 --- Nsubcl Number of subclusters (1)
161-168 F8.3 10+35W L500 0.2-2.3keV luminosity within R500
(in 1042erg/s)
170-177 F8.3 10+35W e_L500 1sigma lower limit of L500 (in 1042erg/s)
179-186 F8.3 10+35W E_L500 1sigma upper limit of L500 (in 1042erg/s)
188-194 F7.5 --- ScaleVal Scaling value
196-203 F8.6 --- MaskFrac Masking fraction
205-219 F15.11 --- lambda Optical richness
221-235 F15.12 --- e_lambda Richness error
237-244 F8.6 --- mu Mass ratio (2)
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Note (1): The number of subclusters also includes the 'main' cluster.
Note (2): mu is the mass ratio between the main cluster and the largest
infalling subcluster.
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Byte-by-byte Description of file: members.dat
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Bytes Format Units Label Explanations
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1- 20 I20 --- Cluster Cluster id
22- 36 I15 --- Galaxy Galaxy id
38- 45 F8.6 --- z Cluster redshift
47- 61 F15.11 deg RAdeg Galaxy right ascension (J2000)
63- 77 F15.11 deg DEdeg Galaxy declination (J2000)
79- 86 F8.6 --- pvalue redMaPPer p-value
88 I1 --- CG [0/1] True (1) if a central galaxy
90 I1 --- label [0/8] Subcluster label
92-108 F17.15 --- Prob HDBSCAN p-value
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Acknowledgements:
Ramus Tuomainen, rasmus.tuomainen(at)helsinki.fi
License: CC-BY-4.0
(End) Patricia Vannier [CDS] 27-Apr-2026