Are mergers responsible for universal halo properties?

Wang, Jie; White, Simon D. M.

doi:10.1111/j.1365-2966.2009.14755.x

Cited by 76 publications

(84 citation statements)

References 64 publications

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“…However, this does not mean that mergers are the only way to generate such distributions. As has been shown recently by Wang & White (2009) even hot dark matter simulations which have almost no mergers show such AMDs. Hence, the origin of the universal form is more generally related to the virialization processes such as the violent relaxation.…”

Section: Discussionsupporting

confidence: 62%

On the Origin of the Angular Momentum Properties of Gas and Dark Matter in Galactic Halos and Its Implications

Sharma

Steinmetz

Bland-Hawthorn

2012

ApJ

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We perform a set of non-radiative hydrodynamical simulations of merging spherical halos in order to understand the angular momentum (AM) properties of the galactic halos seen in cosmological simulations. The universal shape of AM distributions seen in simulations is found to be generically produced as a result of mergers. The universal shape is such that it has an excess of low AM material and hence cannot explain the exponential structure of disk galaxies. A resolution to this is suggested by the spatial distribution of low AM material which is found to be in the center and a conical region close to the axis of rotation. A mechanism that preferentially discards the material in the center and prevents the material along the poles from falling onto the disk is proposed as a solution. We implement a simple geometric criterion for the selective removal of low AM material and show that in order for 90% of halos to host exponential disks one has to reject at least 40% of material. Next, we explore the physical mechanisms responsible for distributing the AM within the halo during a merger. For dark matter there is an inside-out transfer of AM, whereas for gas there is an outside-in transfer, which is due to differences between collisionless and gas dynamics. This is responsible for the spin parameter λ and the shape parameter α of AM distributions being higher for gas compared to dark matter. We also explain the apparent high spin of dark matter halos undergoing mergers and show that a criterion stricter than what is currently used would be required to detect such unrelaxed halos. Finally, we demonstrate that the misalignment of AM between gas and dark matter only occurs when the intrinsic spins of the merging halos are not aligned with the orbital AM of the system. The self-misalignment (orientation of AM when measured in radial shells not being constant), which could be the cause of warps and anomalous rotation in disks galaxies, also occurs under similar conditions. The frequency and amplitude of this misalignment are roughly consistent with the properties of warps seen in disk galaxies.

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Section: Discussionsupporting

confidence: 62%

On the Origin of the Angular Momentum Properties of Gas and Dark Matter in Galactic Halos and Its Implications

Sharma

Steinmetz

Bland-Hawthorn

2012

ApJ

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“…In the past few years, many studies based on Chandra and XMM observations have shown that in general galaxy clusters exhibit elliptical surface brightness maps. Simulations have also predicted that dark matter halos show axis ratios typically of the order of ≈0.8 (Wang & White 2009), thereby disproving the spherical geometry assumption usually adopted (Reiprich & Boringer 2002;Bonamente et al 2006;Shang et al 2009). In this line, the first determination of the intrinsic threedimensional (3D) shapes of galaxy clusters was presented by Morandi et al (2010) by combining X-ray, weak-lensing, and strong-lensing observations.…”

Section: Introductionmentioning

confidence: 96%

Cosmic distance duality relation and the shape of galaxy clusters

Holanda

Lima

Ribeiro

2011

A&A

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Context. Observations in the cosmological domain are heavily dependent on the validity of the cosmic distance-duality (DD) relation, η = D L (z)(1 + z) 2 /D A (z) = 1, an exact result required by the Etherington reciprocity theorem where D L (z) and D A (z) are, respectively, the luminosity and angular diameter distances. In the limit of very small redshifts D A (z) = D L (z) and this ratio is trivially satisfied. Measurements of Sunyaev-Zeldovich effect (SZE) and X-rays combined with the DD relation have been used to determine D A (z) from galaxy clusters. This combination offers the possibility of testing the validity of the DD relation, as well as determining which physical processes occur in galaxy clusters via their shapes. Aims. We use WMAP (7 years) results by fixing the conventional ΛCDM model to verify the consistence between the validity of DD relation and different assumptions about galaxy cluster geometries usually adopted in the literature. Methods. We assume that η is a function of the redshift parametrized by two different relations: η(z) = 1+η 0 z, and η(z) = 1+η 0 z/(1+z), where η 0 is a constant parameter quantifying the possible departure from the strict validity of the DD relation. In order to determine the probability density function (PDF) of η 0 , we consider the angular diameter distances from galaxy clusters recently studied by two different groups by assuming elliptical (isothermal) and spherical (non-isothermal) β models. The strict validity of the DD relation will occur only if the maximum value of η 0 PDF is centered on η 0 = 0. Results. It was found that the elliptical β model is in good agreement with the data, showing no violation of the DD relation (PDF peaked close to η 0 = 0 at 1σ), while the spherical (non-isothermal) one is only marginally compatible at 3σ. Conclusions. The present results derived by combining the SZE and X-ray surface brightness data from galaxy clusters with the latest WMAP results (7-years) favors the elliptical geometry for galaxy clusters. It is remarkable that a local property like the geometry of galaxy clusters might be constrained by a global argument provided by the cosmic DD relation.

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“…The Galactic halo forms through a process of hierarchical merging, smooth accretion, and violent relaxation [1,22,23]. The central regions of halos, where relaxation processes have ended, are in quasi-static equilibrium [24].…”

Section: Equilibrium Dark Matter Distributionsmentioning

confidence: 99%

Dark matter at the end of the Galaxy

et al. 2011

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Dark matter density profiles based upon ΛCDM cosmology motivate an ansatz velocity distribution function with fewer high velocity particles than the Maxwell-Boltzmann distribution or proposed variants. The high velocity tail of the distribution is determined by the outer slope of the dark matter halo -the large radius behavior of the Galactic dark matter density. N-body simulations of Galactic halos reproduce the high velocity behavior of this ansatz. Predictions for direct detection rates are dramatically affected for models where the threshold scattering velocity is within 30% of the escape velocity.

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Are mergers responsible for universal halo properties?

Cited by 76 publications

References 64 publications

On the Origin of the Angular Momentum Properties of Gas and Dark Matter in Galactic Halos and Its Implications

On the Origin of the Angular Momentum Properties of Gas and Dark Matter in Galactic Halos and Its Implications

Cosmic distance duality relation and the shape of galaxy clusters

Dark matter at the end of the Galaxy

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