Galaxy cluster mass reconstruction project - III. The impact of dynamical substructure on cluster mass estimates

L. Old, R. Wojtak, F. R. Pearce, M. E. Gray, G. A. Mamon, C. Sifón, E. Tempel, A. Biviano, H. K.C. Yee, R. de Carvalho, V. Müller, T. Sepp, R. A. Skibba, D. Croton, S. P. Bamford, C. Power, A. von der Linden, A. Saro

Research output: Contribution to journalArticle

  • 3 Citations

Abstract

With the advent of wide-field cosmological surveys, we are approaching samples of hundreds of thousands of galaxy clusters. While such large numbers will help reduce statistical uncertainties, the control of systematics in cluster masses is crucial. Here we examine the effects of an important source of systematic uncertainty in galaxy-based cluster mass estimation techniques: the presence of significant dynamical substructure. Dynamical substructure manifests as dynamically distinct subgroups in phase-space, indicating an 'unrelaxed' state. This issue affects around a quarter of clusters in a generally selected sample. We employ a set of mock clusters whose masses have been measured homogeneously with commonly used galaxy-based mass estimation techniques (kinematic, richness, caustic, radial methods). We use these to study how the relation between observationally estimated and true cluster mass depends on the presence of substructure, as identified by various popular diagnostics.We find that the scatter for an ensemble of clusters does not increase dramatically for clusters with dynamical substructure. However, we find a systematic bias for all methods, such that clusters with significant substructure have higher measured masses than their relaxed counterparts. This bias depends on cluster mass: the most massive clusters are largely unaffected by the presence of significant substructure, but masses are significantly overestimated for lower mass clusters, by ~10 per cent at 1014 and ≳20 per cent for ≲1013.5. The use of cluster samples with different levels of substructure can therefore bias certain cosmological parameters up to a level comparable to the typical uncertainties in current cosmological studies.

LanguageEnglish
Article numberstx3241
Pages853-866
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Volume475
Issue number1
DOIs
StatePublished - 21 Mar 2018

Fingerprint

substructures
galaxies
estimates
project
field survey
kinematics
subgroups
alkalies

Cite this

Old, L., Wojtak, R., Pearce, F. R., Gray, M. E., Mamon, G. A., Sifón, C., ... Saro, A. (2018). Galaxy cluster mass reconstruction project - III. The impact of dynamical substructure on cluster mass estimates. Monthly Notices of the Royal Astronomical Society, 475(1), 853-866. [stx3241]. DOI: 10.1093/mnras/stx3241
Old, L. ; Wojtak, R. ; Pearce, F. R. ; Gray, M. E. ; Mamon, G. A. ; Sifón, C. ; Tempel, E. ; Biviano, A. ; Yee, H. K.C. ; de Carvalho, R. ; Müller, V. ; Sepp, T. ; Skibba, R. A. ; Croton, D. ; Bamford, S. P. ; Power, C. ; von der Linden, A. ; Saro, A./ Galaxy cluster mass reconstruction project - III. The impact of dynamical substructure on cluster mass estimates. In: Monthly Notices of the Royal Astronomical Society. 2018 ; Vol. 475, No. 1. pp. 853-866
@article{a2aedf9fbdc74570ac29e5ac11d50071,
title = "Galaxy cluster mass reconstruction project - III. The impact of dynamical substructure on cluster mass estimates",
abstract = "With the advent of wide-field cosmological surveys, we are approaching samples of hundreds of thousands of galaxy clusters. While such large numbers will help reduce statistical uncertainties, the control of systematics in cluster masses is crucial. Here we examine the effects of an important source of systematic uncertainty in galaxy-based cluster mass estimation techniques: the presence of significant dynamical substructure. Dynamical substructure manifests as dynamically distinct subgroups in phase-space, indicating an 'unrelaxed' state. This issue affects around a quarter of clusters in a generally selected sample. We employ a set of mock clusters whose masses have been measured homogeneously with commonly used galaxy-based mass estimation techniques (kinematic, richness, caustic, radial methods). We use these to study how the relation between observationally estimated and true cluster mass depends on the presence of substructure, as identified by various popular diagnostics.We find that the scatter for an ensemble of clusters does not increase dramatically for clusters with dynamical substructure. However, we find a systematic bias for all methods, such that clusters with significant substructure have higher measured masses than their relaxed counterparts. This bias depends on cluster mass: the most massive clusters are largely unaffected by the presence of significant substructure, but masses are significantly overestimated for lower mass clusters, by ~10 per cent at 1014 and ≳20 per cent for ≲1013.5. The use of cluster samples with different levels of substructure can therefore bias certain cosmological parameters up to a level comparable to the typical uncertainties in current cosmological studies.",
keywords = "Cosmological parameters, Galaxies: Clusters: General, Galaxies: Groups: General, Galaxies: Haloes, Galaxies: Kinematics and dynamics, Large-scale structure of Universe",
author = "L. Old and R. Wojtak and Pearce, {F. R.} and Gray, {M. E.} and Mamon, {G. A.} and C. Sif{\'o}n and E. Tempel and A. Biviano and Yee, {H. K.C.} and {de Carvalho}, R. and V. M{\"u}ller and T. Sepp and Skibba, {R. A.} and D. Croton and Bamford, {S. P.} and C. Power and {von der Linden}, A. and A. Saro",
year = "2018",
month = "3",
day = "21",
doi = "10.1093/mnras/stx3241",
language = "English",
volume = "475",
pages = "853--866",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "OXFORD UNIV PRESS UNITED KINGDOM",
number = "1",

}

Old, L, Wojtak, R, Pearce, FR, Gray, ME, Mamon, GA, Sifón, C, Tempel, E, Biviano, A, Yee, HKC, de Carvalho, R, Müller, V, Sepp, T, Skibba, RA, Croton, D, Bamford, SP, Power, C, von der Linden, A & Saro, A 2018, 'Galaxy cluster mass reconstruction project - III. The impact of dynamical substructure on cluster mass estimates' Monthly Notices of the Royal Astronomical Society, vol. 475, no. 1, stx3241, pp. 853-866. DOI: 10.1093/mnras/stx3241

Galaxy cluster mass reconstruction project - III. The impact of dynamical substructure on cluster mass estimates. / Old, L.; Wojtak, R.; Pearce, F. R.; Gray, M. E.; Mamon, G. A.; Sifón, C.; Tempel, E.; Biviano, A.; Yee, H. K.C.; de Carvalho, R.; Müller, V.; Sepp, T.; Skibba, R. A.; Croton, D.; Bamford, S. P.; Power, C.; von der Linden, A.; Saro, A.

In: Monthly Notices of the Royal Astronomical Society, Vol. 475, No. 1, stx3241, 21.03.2018, p. 853-866.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Galaxy cluster mass reconstruction project - III. The impact of dynamical substructure on cluster mass estimates

AU - Old,L.

AU - Wojtak,R.

AU - Pearce,F. R.

AU - Gray,M. E.

AU - Mamon,G. A.

AU - Sifón,C.

AU - Tempel,E.

AU - Biviano,A.

AU - Yee,H. K.C.

AU - de Carvalho,R.

AU - Müller,V.

AU - Sepp,T.

AU - Skibba,R. A.

AU - Croton,D.

AU - Bamford,S. P.

AU - Power,C.

AU - von der Linden,A.

AU - Saro,A.

PY - 2018/3/21

Y1 - 2018/3/21

N2 - With the advent of wide-field cosmological surveys, we are approaching samples of hundreds of thousands of galaxy clusters. While such large numbers will help reduce statistical uncertainties, the control of systematics in cluster masses is crucial. Here we examine the effects of an important source of systematic uncertainty in galaxy-based cluster mass estimation techniques: the presence of significant dynamical substructure. Dynamical substructure manifests as dynamically distinct subgroups in phase-space, indicating an 'unrelaxed' state. This issue affects around a quarter of clusters in a generally selected sample. We employ a set of mock clusters whose masses have been measured homogeneously with commonly used galaxy-based mass estimation techniques (kinematic, richness, caustic, radial methods). We use these to study how the relation between observationally estimated and true cluster mass depends on the presence of substructure, as identified by various popular diagnostics.We find that the scatter for an ensemble of clusters does not increase dramatically for clusters with dynamical substructure. However, we find a systematic bias for all methods, such that clusters with significant substructure have higher measured masses than their relaxed counterparts. This bias depends on cluster mass: the most massive clusters are largely unaffected by the presence of significant substructure, but masses are significantly overestimated for lower mass clusters, by ~10 per cent at 1014 and ≳20 per cent for ≲1013.5. The use of cluster samples with different levels of substructure can therefore bias certain cosmological parameters up to a level comparable to the typical uncertainties in current cosmological studies.

AB - With the advent of wide-field cosmological surveys, we are approaching samples of hundreds of thousands of galaxy clusters. While such large numbers will help reduce statistical uncertainties, the control of systematics in cluster masses is crucial. Here we examine the effects of an important source of systematic uncertainty in galaxy-based cluster mass estimation techniques: the presence of significant dynamical substructure. Dynamical substructure manifests as dynamically distinct subgroups in phase-space, indicating an 'unrelaxed' state. This issue affects around a quarter of clusters in a generally selected sample. We employ a set of mock clusters whose masses have been measured homogeneously with commonly used galaxy-based mass estimation techniques (kinematic, richness, caustic, radial methods). We use these to study how the relation between observationally estimated and true cluster mass depends on the presence of substructure, as identified by various popular diagnostics.We find that the scatter for an ensemble of clusters does not increase dramatically for clusters with dynamical substructure. However, we find a systematic bias for all methods, such that clusters with significant substructure have higher measured masses than their relaxed counterparts. This bias depends on cluster mass: the most massive clusters are largely unaffected by the presence of significant substructure, but masses are significantly overestimated for lower mass clusters, by ~10 per cent at 1014 and ≳20 per cent for ≲1013.5. The use of cluster samples with different levels of substructure can therefore bias certain cosmological parameters up to a level comparable to the typical uncertainties in current cosmological studies.

KW - Cosmological parameters

KW - Galaxies: Clusters: General

KW - Galaxies: Groups: General

KW - Galaxies: Haloes

KW - Galaxies: Kinematics and dynamics

KW - Large-scale structure of Universe

UR - http://www.scopus.com/inward/record.url?scp=85041336636&partnerID=8YFLogxK

U2 - 10.1093/mnras/stx3241

DO - 10.1093/mnras/stx3241

M3 - Article

VL - 475

SP - 853

EP - 866

JO - Monthly Notices of the Royal Astronomical Society

T2 - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 1

M1 - stx3241

ER -

Old L, Wojtak R, Pearce FR, Gray ME, Mamon GA, Sifón C et al. Galaxy cluster mass reconstruction project - III. The impact of dynamical substructure on cluster mass estimates. Monthly Notices of the Royal Astronomical Society. 2018 Mar 21;475(1):853-866. stx3241. Available from, DOI: 10.1093/mnras/stx3241