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.
| Language | English |
|---|---|
| Article number | stx3241 |
| Pages | 853-866 |
| Number of pages | 14 |
| Journal | Monthly Notices of the Royal Astronomical Society |
| Volume | 475 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 21 Mar 2018 |
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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 journal › Article
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 -