Modelling the shapes of the largest gravitationally bound objects

Rossi, Graziano; Sheth, Ravi K.; Tormen, Giuseppe

doi:10.1111/j.1365-2966.2011.19028.x

Cited by 22 publications

(28 citation statements)

References 162 publications

(286 reference statements)

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“…At high halo masses, the convex hull Lagrange volume approaches a sphere, and the ratio therefore approaches that of a cube enclosing a sphere: 6/π 1.9 (shown as the gray dashed line). Lower halo masses, however, tend to have more elongated Lagrange volumes (Rossi et al 2011). For these halos, the angle between the simulation axes and the elongation axis can strongly inflate the value of the (unrotated) cuboid volume V. The scatter in the bottom panel is thus dominated by the scatter in the cuboid volume, which reflects both the position of the traceback particles and their alignment with the axis of the simulation, and decreases with increasing halo mass.…”

Section: Identifying the Lagrange Volumementioning

confidence: 99%

How to zoom: bias, contamination and Lagrange volumes in multimass cosmological simulations

Oñorbe

Garrison-Kimmel

Maller

et al. 2013

Monthly Notices of the Royal Astronomical Society

150

142

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We perform a suite of multimass cosmological zoom simulations of individual dark matter halos and explore how to best select Lagrangian regions for resimulation without contaminating the halo of interest with low-resolution particles. Such contamination can lead to significant errors in the gas distribution of hydrodynamical simulations, as we show. For a fixed Lagrange volume, we find that the chance of contamination increases systematically with the level of zoom. In order to avoid contamination, the Lagrangian volume selected for resimulation must increase monotonically with the resolution difference between parent box and the zoom region. We provide a simple formula for selecting Lagrangian regions (in units of the halo virial volume) as a function of the level of zoom required. We also explore the degree to which a halo's Lagrangian volume correlates with other halo properties (concentration, spin, formation time, shape, etc.) and find no significant correlation. There is a mild correlation between Lagrange volume and environment, such that halos living in the most clustered regions have larger Lagrangian volumes. Nevertheless, selecting halos to be isolated is not the best way to ensure inexpensive zoom simulations. We explain how one can safely choose halos with the smallest Lagrangian volumes, which are the least expensive to resimulate, without biasing one's sample.

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Section: Identifying the Lagrange Volumementioning

confidence: 99%

How to zoom: bias, contamination and Lagrange volumes in multimass cosmological simulations

Oñorbe

Garrison-Kimmel

Maller

et al. 2013

Monthly Notices of the Royal Astronomical Society

150

142

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“…From the theoretical perspective, there is a gap in our knowledge about the way in which dark matter haloes acquire their shape and, in particular, on the impact of the dynamics of the surrounding large‐scale structure in the non‐linear regime (Lee, Jing & Suto 2005; Betancort‐Rijo & Trujillo 2009; Rossi, Sheth & Tormen 2010; Salvador‐Solé et al 2011). Indeed, most of the theoretical works cited above restrict their analysis to the present‐day correlations with the environment, and do not consider when the shapes have been established and how they relate to the past history of an object.…”

Section: Introductionmentioning

confidence: 99%

The shape of dark matter haloes in the Aquarius simulations: evolution and memory

Vera-Ciro¹,

Sales²,

Helmi³

et al. 2011

Monthly Notices of the Royal Astronomical Society

169

193

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We use the high‐resolution cosmological N‐body simulations from the Aquarius project to investigate in detail the mechanisms that determine the shape of Milky Way type dark matter haloes. We find that, when measured at the instantaneous virial radius, the shape of individual haloes changes with time, evolving from a typically prolate configuration at early stages to a more triaxial/oblate geometry at the present day. This evolution in halo shape correlates well with the distribution of the infalling material: prolate configurations arise when haloes are fed through narrow filaments, which characterizes the early epochs of halo assembly, whereas triaxial/oblate configurations result as the accretion turns more isotropic at later times. Interestingly, at redshift z= 0, clear imprints of the past history of each halo are recorded in their shapes at different radii, which also exhibit a variation from prolate in the inner regions to triaxial/oblate in the outskirts. Provided that the Aquarius haloes are fair representatives of Milky Way like 1012 M⊙ objects, we conclude that the shape of such dark matter haloes is a complex, time‐dependent property, with each radial shell retaining memory of the conditions at the time of collapse.

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“…Thus, it is natural to believe that the shape of peaks is somehow translated into that of haloes, in agreement with the above‐mentioned alignments. A few authors (Lee, Jing & Suto ; Rossi, Sheth & Tormen ) have tried to make the link between the shape of haloes and that of peaks through the modelling of ellipsoidal collapse. Unfortunately, these models do not account for the highly non‐linear effects of shell crossing during virialization, which play a crucial role in setting the final properties of virialized haloes.…”

Section: Introductionmentioning

confidence: 99%

Theoretical dark matter halo kinematics and triaxial shape

Salvador-Solé

Serra

Manrique

et al. 2012

Monthly Notices of the Royal Astronomical Society

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In a recent paper, Salvador-Solé et al. have derived the typical inner structure of dark matter haloes from that of peaks in the initial random Gaussian density field, determined by the power spectrum of density perturbations characterizing the hierarchical cosmology under consideration. In this paper, we extend this formalism to the typical kinematics and triaxial shape of haloes. Specifically, we establish the link between such halo properties and the power spectrum of density perturbations through the typical shape of peaks. The trends of the predicted typical halo shape, pseudo-phase-space density and anisotropy profiles are in good agreement with the results of numerical simulations. Our model sheds light on the origin of the power-law-like pseudo-phase-space density profile for virialized haloes.Key words: methods: analytic -galaxies: haloes -cosmology: theory -dark matter. I N T RO D U C T I O NVirialized haloes in N-body simulations of cold dark matter (CDM) cosmologies show a wide variety of ellipsoidal shapes. On the contrary, their structural and kinematic properties are remarkably similar from one object to another. They are little sensitive not only to the mass, redshift, environment and even specific cosmology, but also to their individual shape. Only their scaling shows a mild dependence on some of these properties. As shown by gravohydrodynanic simulations, baryons introduce a larger scatter in the properties of haloes at their central region. However, in this paper, we will concentrate on pure dark matter haloes and we will not deal with such secondary baryonic effects.The typical spherically averaged halo density profile, ρ (r), is well fitted, down to about one-hundredth the virial radius, by the so-called NFW profile (Navarro, Frenk & White 1997) as well as by the Einasto (1965) profile, which gives slightly better fits down to smaller radii (Navarro et al. 2004;Merritt et al. 2005Merritt et al. , 2006Stadel et al. 2009;Navarro et al 2010). The velocity dispersion profile, σ (r), is reasonably well fitted by the solution of the Jeans equation for spherically symmetric isotropic systems with null value at infinity (Cole & Lacey 1996;Merritt et al. 2006). More remarkably, Taylor & Navarro (2001) showed that the pseudo-phase-space density profile is very nearly a pure power law, (1), σ (r) is the velocity dispersion over the whole spherical shell with r, so the variance coincides with the spherical average of the local value at points with r, σ 2 (r) = σ 2 loc (r). Finally, Hansen & Moore (2006) found that the velocity anisotropy profile β(r) behaves linearly with the logarithmic derivative of the density,with a and b, respectively, equal to about −0.2 and 0.8 (Hansen & Stadel 2006; see also Ludlow et al. 2011 for an alternative expression), although with a substantial scatter this time.The origin of all these trends is certainly related with the way dark matter clusters. In hierarchical cosmologies, haloes grow through continuous mergers with notably different dynamic effects accordin...

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Modelling the shapes of the largest gravitationally bound objects

Cited by 22 publications

References 162 publications

How to zoom: bias, contamination and Lagrange volumes in multimass cosmological simulations

How to zoom: bias, contamination and Lagrange volumes in multimass cosmological simulations

The shape of dark matter haloes in the Aquarius simulations: evolution and memory

Theoretical dark matter halo kinematics and triaxial shape

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