Mass profiles and galaxy orbits in nearby galaxy clusters from the analysis of the projected phase space

Wojtak, Radosław; Łokas, Ewa L.

doi:10.1111/j.1365-2966.2010.17297.x

Cited by 80 publications

(110 citation statements)

References 85 publications

(215 reference statements)

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“…Kinematical modelers attempt to throw out the high-velocity interlopers by identifying this gap by eye (Kent & Gunn 1982;Łokas & Mamon 2003) or automatically (Fadda et al 1996) or by rejecting 3σ outliers, either using a global criterion (Yahil & Vidal 1977) or a local one (e.g. Łokas et al 2006;Wojtak & Łokas 2010). Interestingly, the 3σ v criterion was first motivated on statistical grounds, but the v 2.0 v v inflection point one sees in the plots of Fig.…”

Section: Global Statisticsmentioning

confidence: 99%

The universal distribution of halo interlopers in projected phase space

Mamon

Biviano

Murante

2010

A&A

106

149

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When clusters of galaxies are viewed in projection, one cannot avoid picking up a fraction of foreground/background interlopers, that lie within the virial cone, but outside the virial sphere. Structural and kinematic deprojection equations are known for the academic case of a static Universe, but not for the real case of an expanding Universe, where the Hubble flow (HF) stretches the line-of-sight distribution of velocities. Using 93 mock relaxed clusters, built from the dark matter (DM) particles of a hydrodynamical cosmological simulation, we quantify the distribution of interlopers in projected phase space (PPS), as well as the biases in the radial and kinematical structure of clusters produced by the HF. The stacked mock clusters are well fit by an m = 5 Einasto DM density profile (but only out to 1.5 virial radii), with velocity anisotropy (VA) close to the Mamon-Łokas model with characteristic radius equal to that of density slope −2. The surface density of interlopers is nearly flat out to the virial radius, while their velocity distribution shows a dominant Gaussian cluster-outskirts component and a flat field component. This distribution of interlopers in PPS is nearly universal, showing only small trends with cluster mass, and is quantified. A local κ = 2.7 sigma velocity cut is found to return the line-ofsight velocity dispersion profile (LOSVDP) expected from the NFW density and VA profiles measured in three dimensions. The HF causes a shallower outer LOSVDP that cannot be well matched by the Einasto model for any value of κ. After this velocity cut, which removes 1 interloper out of 6, interlopers still account for 23 ± 1% of all DM particles with projected radii within the virial radius (surprisingly very similar to the observed fraction of cluster galaxies lying off the Red Sequence) and over 60% between 0.8 and 1 virial radius. The HF causes the best-fit projected NFW or m = 5 Einasto model to the stacked cluster to underestimate the true concentration measured in 3D by 6 ± 6% (16 ± 7%) after (before) the velocity cut. These biases in concentration are reduced by over a factor two once a constant background is included in the fit. The VA profile recovered from the measured LOSVDP by assuming the correct mass profile recovers fairly well the VA measured in 3D, with a slight, marginally significant, bias towards more radial orbits in the outer regions. These small biases in the concentration and VA of the galaxy system are overshadowed by important cluster-to-cluster fluctuations caused by cosmic variance and by the strong inefficiency caused by the limited numbers of observed galaxies in clusters. An appendix provides an analytical approximation to the surface density, projected mass and tangential shear profiles of the Einasto model. Another derives the expressions for the surface density and mass profiles of the NFW model projected on the sphere (for future kinematic modeling).

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Section: Global Statisticsmentioning

confidence: 99%

The universal distribution of halo interlopers in projected phase space

Mamon

Biviano

Murante

2010

A&A

106

149

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“…Several X-ray and other studies studies have found that the mass of A2142 is approximately M = 0.9 × 10 15 h −1 M (Okabe & Umetsu 2008;Umetsu et al 2009;Wojtak & Łokas 2010;Munari et al 2014;Shan et al 2015). Munari et al (2014) compared several mass estimation methods and concluded that the mass of the cluster is M 200 = 0.875 × 10 15 h −1 M (if recalculated to the Hubble parameter H 0 = 100 h km s −1 Mpc −1 , as used in our paper); this value is 0.965 times lower than the dynamical mass of A2142 as calculated in Tempel et al (2014b).…”

Section: Abell Cluster A2142mentioning

confidence: 99%

Unusual A2142 supercluster with a collapsing core: distribution of light and mass

Einasto

Gramann

Saar

et al. 2015

A&A

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Context. Superclusters of galaxies can be used to test cosmological models of the formation and evolution of the largest structures in the cosmic web, and of galaxy and cluster evolution in superclusters. Aims. We study the distribution, masses, and dynamical properties of galaxy groups in the A2142 supercluster. Methods. We analyse the global luminosity density distribution in the supercluster and divide the supercluster into the high-density core and the low-density outskirts regions. We find galaxy groups and filaments in these regions, calculate their masses and mass-tolight ratios and analyse their dynamical state with 1D and 3D statistics. We use the spherical collapse model to study the dynamical state of the supercluster. Results. In the A2142 supercluster rich groups and clusters lie along an almost straight line forming the 50 h −1 Mpc long main body of the supercluster. The A2142 supercluster has a very high density core surrounded by lower-density outskirts. The total estimated mass of the supercluster is M est = 6.2 × 10 15 M . More than a half of groups with at least ten member galaxies in the supercluster lie in the high-density core of the supercluster, centred at the X-ray cluster A2142. Most of the groups in the core region are multimodal. In the outskirts of the supercluster, the number of groups is larger than in the core, and groups are poorer. The orientation of the axis of the cluster A2142 follows the orientations of its X-ray substructures and radio halo, and is aligned along the supercluster axis. The high-density core of the supercluster with the global density D8 ≥ 17 and perhaps with D8 ≥ 13 may have started to collapse. Conclusions. A2142 supercluster with collapsing core and straight body, is an unusual object among superclusters. In the course of the future evolution, the supercluster may split into several systems.

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“…Observational constraints on the spherical anisotropy β in individual clusters exhibit a huge variety of profiles (Benatov et al 2006;Hwang & Lee 2008;Wojtak & Lokas 2010;Wojtak et al 2009). Some measurements are far outside the margins allowed by the spherically averaged profiles of simulated clusters (see e.g.…”

Section: Observational Constraints On βmentioning

confidence: 99%

“…It plays a key role in dynamical modelling of kinematical data of objects at all scales, from the stellar halo of the Milky Way (Kafle et al 2012), dwarf spheroidals ( Lokas 2009;Walker et al 2009), to elliptical galaxies (Dekel et al 2005;Napolitano et al 2011;Wojtak & Mamon 2012) and galaxy clusters (Biviano & Girardi 2003;Wojtak & Lokas 2010). Prior knowledge on the anisotropy or elaborated techniques of data analysis are essential for accurate and unbiased mass estimates.…”

Section: Introductionmentioning

confidence: 99%

Orbital anisotropy in cosmological haloes revisited

Wojtak

Gottlöber

Klypin

2013

Monthly Notices of the Royal Astronomical Society

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The velocity anisotropy of particles inside dark matter (DM) haloes is an important physical quantity, which is required for the accurate modelling of mass profiles of galaxies and clusters of galaxies. It is typically measured using the ratio of the radialto-tangential velocity dispersions at a given distance from the halo centre. However, this measure is insufficient to describe the dynamics of realistic haloes, which are not spherical and are typically quite elongated. Studying the velocity distribution in massive DM haloes in cosmological simulations, we find that in the inner parts of the haloes the local velocity ellipsoids are strongly aligned with the major axis of the halo, the alignment being stronger for more relaxed haloes. In the outer regions of the haloes, the alignment becomes gradually weaker and the orientation is more random. These two distinct regions of different degree of the alignment coincide with two characteristic regimes of the DM density profile: a shallow inner cusp and a steep outer profile that are separated by a characteristic radius at which the density declines as ρ ∝ r −2 . This alignment of the local velocity ellipsoids requires reinterpretation of features found in measurements based on the spherically averaged ratio of the radial-to-tangential velocity dispersions. In particular, we show that the velocity distribution in the central halo regions is highly anisotropic. For cluster-size haloes with mass 10 14 − 10 15 h −1 M ⊙ , the velocity anisotropy along the major axis is nearly independent of radius and is equal to β = 1 − σ 2 perp /σ 2 radial ≈ 0.4, which is significantly larger than the previously estimated spherically averaged velocity anisotropy. The alignment of density and velocity anisotropies, and the radial trends may also have some implications for the mass modelling based on kinematical data of such objects as galaxy clusters or dwarf spheroidals, where the orbital anisotropy is a key element in an unbiased mass inference.

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Mass profiles and galaxy orbits in nearby galaxy clusters from the analysis of the projected phase space

Cited by 80 publications

References 85 publications

The universal distribution of halo interlopers in projected phase space

The universal distribution of halo interlopers in projected phase space

Unusual A2142 supercluster with a collapsing core: distribution of light and mass

Orbital anisotropy in cosmological haloes revisited

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