Asymmetric velocity anisotropies in remnants of collisionless mergers

Sparre, Martin; Hansen, Steen H.

doi:10.1088/1475-7516/2012/07/042

Cited by 15 publications

(12 citation statements)

References 66 publications

(100 reference statements)

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“…For the merger remnant β is roughly constant and positive along the major axis and monotonically increasing along the minor axis. This behaviour is consistent with our previous study of major mergers [26]. The instability simulation gives a complicated behaviour of both β, ρ and the axis ratios.…”

Section: Category 2: Haloes With Complex β-Profilessupporting

confidence: 92%

“…The spherically averaged velocity anisotropy profiles of the merger remnants (simulation IV) are typically increasing from β = 0 in the center of the halo out to the radius with β = 0.3, where a maximum appears. This behaviour is similar to many cosmological haloes [11], and in agreement with what is reported in other studies of merger remnants [19,26,44].…”

Section: Velocity Anisotropy Profilessupporting

confidence: 92%

“…The haloes still have freedom to have different β-profiles in different directions as long as the spherically averaged profiles obey this relation. An example of a halo in which the β-γ relation is not obeyed through cones in different directions, but only in spherically averaged bins, has been presented in the study of merger remnants in [26].…”

Section: An Overview: Which Structures Are On the Attractor?mentioning

confidence: 99%

“…There exists evidence that β-profiles are not spherically symmetric functions (or functions that are constant along density or potential contours, if the structure is non-spherical) in all dark matter haloes. In a detailed study of remnants of collisionless mergers, it has been shown that the velocity anisotropy profiles of merger remnants exhibit different behaviour depending on whether they are calculated along the major or the minor axis [26]. The behaviour of β were clearly correlated with the shape and the orientation of the haloes, in such a way that the largest velocity anisotropy was found along the major axis.…”

Section: Introductionmentioning

confidence: 99%

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The behaviour of shape and velocity anisotropy in dark matter haloes

Sparre

Hansen

2012

J. Cosmol. Astropart. Phys.

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Dark matter haloes from cosmological N-body simulations typically have triaxial shapes and anisotropic velocity distributions. Recently it has been shown that the velocity anisotropy, β, of cosmological haloes and major merger remnants depends on direction in such a way that β is largest along the major axis and smallest along the minor axis. In this work we use a wide range of non-cosmological N-body simulations to examine halo shapes and direction-dependence of velocity anisotropy profiles. For each of our simulated haloes we define 48 cones pointing in different directions, and from the particles inside each cone we compute velocity anisotropy profiles. We find that elongated haloes can have very distinct velocity anisotropies. We group the behaviour of haloes into three different categories, that range from spherically symmetric profiles to a much more complex behaviour, where significant differences are found for β along the major and minor axes. We encourage future studies of velocity anisotropies in haloes from cosmological simulations to calculate β-profiles in cones, since it reveals information, which is hidden from a spherically averaged profile. Finally, we show that spherically averaged profiles often obey a linear relation between β and the logarithmic density slope in the inner parts of haloes, but this relation is not necessarily obeyed, when properties are calculated in cones.

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Section: Category 2: Haloes With Complex β-Profilessupporting

confidence: 92%

Section: Velocity Anisotropy Profilessupporting

confidence: 92%

Section: An Overview: Which Structures Are On the Attractor?mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The behaviour of shape and velocity anisotropy in dark matter haloes

Sparre

Hansen

2012

J. Cosmol. Astropart. Phys.

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“…After 20 such perturbations we use the standard value of G, and let the structure relax completely. For further details, see Sparre & Hansen (2012).…”

Section: G-perturbationsmentioning

confidence: 99%

A Derivation of (Half) the Dark Matter Distribution Function

Hansen

Sparre

2012

ApJ

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All dark matter structures appear to follow a set of universalities, such as phase-space density or velocity anisotropy profiles; however, the origin of these universalities remains a mystery. Any equilibrated dark matter structure can be fully described by two functions, namely the radial and tangential velocity distribution functions (VDFs), and once these two are understood we will understand all the observed universalities. Here, we demonstrate that if we know the radial VDF then we can derive and understand the tangential VDF. This is based on simple dynamical arguments about properties of collisionless systems. We use a range of controlled numerical simulations to demonstrate the accuracy of this result. We therefore boil the question of the dark matter structural properties down to understanding the radial VDF.

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Numerical simulations of the dark universe: State of the art and the next decade

Kuhlen

Vogelsberger

Angulo

2012

Physics of the Dark Universe

198

174

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We present a review of the current state of the art of cosmological dark matter simulations, with particular emphasis on the implications for dark matter detection efforts and studies of dark energy. This review is intended both for particle physicists, who may find the cosmological simulation literature opaque or confusing, and for astro-physicists, who may not be familiar with the role of simulations for observational and experimental probes of dark matter and dark energy. Our work is complementary to the contribution by M. Baldi in this issue, which focuses on the treatment of dark energy and cosmic acceleration in dedicated N-body simulations.Truly massive dark matter-only simulations are being conducted on national supercomputing centers, employing from several billion to over half a trillion particles to simulate the formation and evolution of cosmologically representative volumes (cosmic scale) or to zoom in on individual halos (cluster and galactic scale). These simulations cost millions of core-hours, require tens to hundreds of terabytes of memory, and use up to petabytes of disk storage. Predictions from such simulations touch on almost every aspect of dark matter and dark energy studies, and we give a comprehensive overview of this connection. We also discuss the limitations of the cold and collisionless DM-only approach, and describe in some detail efforts to include different particle physics as well as baryonic physics in cosmological galaxy formation simulations, including a discussion of recent results highlighting how the distribution of dark matter in halos may be altered. We end with an outlook for the next decade, presenting our view of how the field can be expected to progress.

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Asymmetric velocity anisotropies in remnants of collisionless mergers

Cited by 15 publications

References 66 publications

The behaviour of shape and velocity anisotropy in dark matter haloes

The behaviour of shape and velocity anisotropy in dark matter haloes

A Derivation of (Half) the Dark Matter Distribution Function

Numerical simulations of the dark universe: State of the art and the next decade

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