The shape of relaxed galaxy clusters and the public release of a HST shape measurement code, pyRRG

Harvey, David J.; Tam, Sut-Ieng; Jauzac, Mathilde; Massey, Richard; Rhodes, Jason

doi:10.48550/arxiv.1911.06333

Cited by 7 publications

(11 citation statements)

References 36 publications

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“…Figure 4 plots the correlation between position angles of DM haloes and BCGs, indicating that they are well aligned. This result is consistent with recent observational results by Harvey et al (2019) which shows that the BCGs and DM haloes are well aligned with each other, and also is qualitatively consistent with those of cluster-sized haloes in the Horizon-AGN simulation shown in Okabe et al (2018). We present further comparison with the Horizon-AGN simulation in Section 4.…”

Section: Ellipticities and Alignment Angles Between Dark Matter Haloe...supporting

confidence: 91%

“…On the other hand, the comparison of position angles shown in Figure 16 indicates that both position angles are well aligned with each other despite the large errors for weak lensing measurements. Although we cannot draw any robust conclusion because weak and strong lensing measure ellipticities at different scales (see also e.g., Oguri et al 2010;Harvey et al 2019, for misalignment between inner and outer DM haloes), this result implies that the strong lensing method might slightly over-estimates ellipticities.…”

Section: Discussionmentioning

confidence: 82%

“…To check this possibility, in Figure 14 we compare ellipticity differences e DM − e BCG with the number of multiple images used for strong lens mass modeling. While the lack of any systematic correlation in Figure 14 suggests that such bias in measured ellipticity values from strong lensing may not be significant, future studies to validate strong lensing methods to measure ellipticities are warranted (see Harvey et al 2019, for another validation test). Another possible systematic effect comes from the number of dark matter haloes that is allowed to vary in strong lens mass modeling.…”

Section: Discussionmentioning

confidence: 99%

“…An important characteristics of galaxy clusters is that they are highly non-spherical. There has been a number of observational studies that measure non-sphericities of galaxy clusters from member galaxy distribution (e.g., Binggeli 1982;West et al 2017), X-ray surface brightness (e.g., Hashimoto et al 2008;Kawahara 2010), gravitational lensing signal (e.g., Oguri et al 2010Oguri et al , 2012Umetsu et al 2018;Harvey et al 2019), and the Sunyaev Zel'dovich effect (e.g., Donahue et al 2016). Furthermore, N-body simulations based on the ΛCDM model also predict non-sphericities of galaxy cluster sized dark matter (DM) haloes (e.g., Jing & Suto 2002).…”

Section: Introductionmentioning

confidence: 99%

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Shapes and alignments of dark matter haloes and their brightest cluster galaxies in 39 strong lensing clusters

Okabe,

Oguri,

Peirani

et al. 2020

Preprint

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We study shapes and alignments of 45 dark matter (DM) haloes and their brightest cluster galaxies (BCGs) using a sample of 39 massive clusters from Hubble Frontier Field (HFF), Cluster Lensing And Supernova survey with Hubble (CLASH), and Reionization Lensing Cluster Survey (RELICS). We measure shapes of the DM haloes by strong gravitational lensing, whereas BCG shapes are derived from their light profiles in Hubble Space Telescope images. Our measurements from a large sample of massive clusters presented here provide new constraints on dark matter and cluster astrophysics. We find that DM haloes are on average highly elongated with the mean ellipticity of 0.482 ± 0.028, and position angles of major axes of DM haloes and their BCGs tend to be aligned well with the mean value of alignment angles of 22.2±3.9 deg. We find that DM haloes in our sample are on average more elongated than their BCGs with the mean difference of their ellipticities of 0.11 ± 0.03. In contrast, the Horizon-AGN cosmological hydrodynamical simulation predicts on average similar ellipticities between DM haloes and their central galaxies. While such a difference between the observations and the simulation may well be explained by the difference of their halo mass scales, other possibilities include the bias inherent to strong lensing measurements, limited knowledge of baryon physics, or a limitation of cold dark matter.

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Section: Ellipticities and Alignment Angles Between Dark Matter Haloe...supporting

confidence: 91%

Section: Discussionmentioning

confidence: 82%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Shapes and alignments of dark matter haloes and their brightest cluster galaxies in 39 strong lensing clusters

Okabe,

Oguri,

Peirani

et al. 2020

Preprint

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“…For mass distributions that appear approximately elliptical in projection, the weak lensing tangential shear is stronger at a given radius along the direction of the major axis of the ellipse compared to the minor axis (e.g., Natarajan & Refregier 2000;. For massive clusters and deep weak lensing data, this effect can be used to constrain halo ellipticities for individual targets (e.g., Oguri et al 2010;Harvey et al 2019), yielding robust ( 5σ) detections of halo ellipticity from joint analyses of larger samples (e.g., Oguri et al 2012;Umetsu et al 2018).…”

mentioning

confidence: 99%

Tightening weak lensing constraints on the ellipticity of galaxy-scale dark matter haloes

Schrabback

Hoekstra

Waerbeke

et al. 2021

A&A

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Cosmological simulations predict that galaxies are embedded into triaxial dark matter haloes, which appear approximately elliptical in projection. Weak gravitational lensing allows us to constrain these halo shapes and thereby test the nature of dark matter. Weak lensing has already provided robust detections of the signature of halo flattening at the mass scales of groups and clusters, whereas results for galaxies have been somewhat inconclusive. Here we combine data from five weak lensing surveys (NGVSLenS, KiDS/KV450, CFHTLenS, CS82, and RCSLenS, listed in order of most to least constraining) in order to tighten observational constraints on galaxy-scale halo ellipticity for photometrically selected lens samples. We constrain fh, the average ratio between the aligned component of the halo ellipticity and the ellipticity of the light distribution, finding fh = 0.303−0.079+0.080 for red lens galaxies and fh = 0.217−0.159+0.160 for blue lens galaxies when assuming elliptical Navarro-Frenk-White density profiles and a linear scaling between halo ellipticity and galaxy ellipticity. Our constraints for red galaxies constitute the currently most significant (3.8σ) systematics-corrected detection of the signature of halo flattening at the mass scale of galaxies. Our results are in good agreement with expectations from the Millennium Simulation that apply the same analysis scheme and incorporate models for galaxy–halo misalignment. Assuming these misalignment models and the analysis assumptions stated above are correct, our measurements imply an average dark matter halo ellipticity for the studied red galaxy samples of ⟨|ϵh|⟩ = 0.174 ± 0.046, where |ϵh| = (1 − q)/(1 + q) relates to the ratio q = b/a of the minor and major axes of the projected mass distribution. Similar measurements based on larger upcoming weak lensing data sets can help to calibrate models for intrinsic galaxy alignments, which constitute an important source of systematic uncertainty in cosmological weak lensing studies.

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Triaxiality in galaxy clusters: Mass versus potential reconstructions

Stapelberg

Tchernin

Hug

et al. 2022

A&A

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Context. Accounting for the triaxial shapes of galaxy clusters will become important in the context of upcoming cosmological surveys. This will provide a challenge given that the density distribution of gas cannot be described by simple geometrical models without loss of information. Aims. We investigate the effects of simple 3D models on cluster gravitational potentials and gas density distribution to determine which of these quantities is most suitable and appropriate for characterising galaxy clusters in cosmological studies. Methods. We use a statistical sample of 85 galaxy clusters from a large cosmological N-body + hydrodynamical simulation to investigate cluster shapes as a function of radius for both gas density and potential. We examine how the resulting parameters are affected by the substructure removal (for the gas density) and by the definition of the computation volume (interior vs. shells). Results. We find that the orientation and axis ratio of gas isodensity contours are degenerate with the presence of substructures and are unstable against fluctuations. Moreover, as the derived cluster shape depends on the method used for removing the substructures, thermodynamic properties extracted from the X-ray emissivity profile, for example, suffer from this additional and often underestimated bias. In contrast, the shapes of the smooth cluster potentials are less affected by fluctuations and converge towards simple geometrical models, both in the case of relaxed and dynamically active clusters. Conclusions. The observation that cluster potentials can be represented better by simple geometrical models and reconstructed with a lower level of systematic error for both dynamically active and relaxed clusters suggests that characterising galaxy clusters by their potential is a promising alternative to using cluster masses in cluster cosmology. With this approach, dynamically active and relaxed clusters could be combined in cosmological studies, improving statistics and lowering scatter.

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The shape of relaxed galaxy clusters and the public release of a HST shape measurement code, pyRRG

Cited by 7 publications

References 36 publications

Shapes and alignments of dark matter haloes and their brightest cluster galaxies in 39 strong lensing clusters

Shapes and alignments of dark matter haloes and their brightest cluster galaxies in 39 strong lensing clusters

Tightening weak lensing constraints on the ellipticity of galaxy-scale dark matter haloes

Triaxiality in galaxy clusters: Mass versus potential reconstructions

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