Concentration, ellipsoidal collapse, and the densest dark matter haloes

Okoli, Chiamaka; Afshordi, Niayesh

doi:10.1093/mnras/stv2905

Cited by 42 publications

(50 citation statements)

References 44 publications

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“…The transition between these two regimes is redshift-dependent, but falls between M and 1000M for 0 ≤ z ≤ 4. Okoli & Afshordi (2016) calculate the initial energy of a region before collapse, then assume energy is conserved and use the Jeans equation to find concentration from the final energy. In the case of spherical collapse (valid for the largest halos), the resulting concentration c ∼ 2.5 is mass-independent.…”

Section: A3 Models Of the C-m Relationmentioning

confidence: 99%

Halo Profiles and the Concentration–Mass Relation for a ΛCDM Universe

Child

Habib

Heitmann

et al. 2018

ApJ

142

154

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Profiles of dark matter-dominated halos at the group and cluster scales play an important role in modern cosmology. Using results from two very large cosmological N-body simulations, which increase the available volume at their mass resolution by roughly two orders of magnitude, we robustly determine the halo concentration-mass (c-M) relation over a wide range of masses, employing multiple methods of concentration measurement. We characterize individual halo profiles, as well as stacked profiles, relevant for galaxy-galaxy lensing and next-generation cluster surveys; the redshift range covered is 0 ≤ z ≤ 4, with a minimum halo mass of M 200c ∼ 2×10 11 M . Despite the complexity of a proper description of a halo (environmental effects, merger history, nonsphericity, relaxation state), when the mass is scaled by the nonlinear mass scale M (z), we find that a simple non-power-law form for the c-M/M relation provides an excellent description of our simulation results across eight decades in M/M and for 0 ≤ z ≤ 4. Over the mass range covered, the c-M relation has two asymptotic forms: an approximate power law below a mass threshold M/M ∼ 500 − 1000, transitioning to a constant value, c 0 ∼ 3 at higher masses. The relaxed halo fraction decreases with mass, transitioning to a constant value of ∼ 0.5 above the same mass threshold. We compare Navarro-Frenk-White (NFW) and Einasto fits to stacked profiles in narrow mass bins at different redshifts; as expected, the Einasto profile provides a better description of the simulation results. At cluster scales at low redshift, however, both NFW and Einasto profiles are in very good agreement with the simulation results, consistent with recent weak lensing observations.

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Section: A3 Models Of the C-m Relationmentioning

confidence: 99%

Halo Profiles and the Concentration–Mass Relation for a ΛCDM Universe

Child

Habib

Heitmann

et al. 2018

ApJ

142

154

View full text Add to dashboard Cite

show abstract

“…While it is encouraging that such different types of models successfully describe the c-M relation, most of them share one shortcoming: whatever physical mechanisms shape concentration are perhaps understood in broad strokes but do not directly inform the functional form of the c-M or c-ν relation (for partial exceptions see Ludlow et al 2014 andOkoli &Afshordi 2016). For example, while it is enlightening to understand that concentration increases with halo age, it is not obvious how concentration evolves as a function of time.…”

Section: Introductionmentioning

confidence: 99%

An Accurate Physical Model for Halo Concentrations

Diemer¹,

Joyce

2019

ApJ

240

189

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The relation between halo mass, M , and concentration, c, is a critical component in our understanding of the structure of dark matter halos. While numerous models for this relation have been proposed, almost none of them attempt to derive the evolution of the relation analytically. We build on previous efforts to model the c-M relation as a function of physical parameters such as the peak height, ν, and the effective power spectrum slope, n eff , which capture the dependence of c on halo mass, redshift, and cosmology. We present three major improvements over previous models. First, we derive an analytical expression for the c-M relation that is valid under the assumption of pseudo-evolution, i.e., assuming that the density profiles of halos are static in physical coordinates while the definition of their boundary evolves. We find that this ansatz is highly successful in describing the evolution of the low-mass end of the c-M relation. Second, we employ a new physical variable, the effective exponent of linear growth, α eff , to parameterize deviations from an Einstein-de Sitter expansion history. Third, we combine an updated definition of n eff with the additional dependence on α eff and propose a phenomenological extension of our analytical framework to include all halo masses. This semianalytical model matches simulated concentrations in both scale-free models and ΛCDM to 5% accuracy with very few exceptions and differs significantly from all previously proposed models. We present a publicly available code to compute the predictions of our model in the python toolkit Colossus, including updated parameters for the model of Diemer and Kravtsov.

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“…One coresponds to the canonical model in Reference [50] which assumes the concentration-mass relation derived in Reference [64]. The other corresponds to the concentration-mass relation in Reference [156]. For both cases, the fitting function of the boost factor is written in a combination of two sigmoid functions, f (x) = (1 + e −ax ) −1 , log 10 B sh = X(z)…”

Section: Conflicts Of Interestmentioning

confidence: 99%

“…Comparisons between the boost factor from our calculations in Reference [50] and the fitting functions in this section. The left panel is the result assuming the concentration-mass relation in Reference [64] while the right panel assuming the relation in Reference [156].…”

Section: Conflicts Of Interestmentioning

confidence: 99%

Halo Substructure Boosts to the Signatures of Dark Matter Annihilation

2019

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The presence of dark matter substructure will boost the signatures of dark matter annihilation. We review recent progress on estimates of this subhalo boost factor—a ratio of the luminosity from annihilation in the subhalos to that originating the smooth component—based on both numerical N-body simulations and semi-analytic modelings. Since subhalos of all the scales, ranging from the Earth mass (as expected, e.g., the supersymmetric neutralino, a prime candidate for cold dark matter) to galaxies or larger, give substantial contribution to the annihilation rate, it is essential to understand subhalo properties over a large dynamic range of more than twenty orders of magnitude in masses. Even though numerical simulations give the most accurate assessment in resolved regimes, extrapolating the subhalo properties down in sub-grid scales comes with great uncertainties—a straightforward extrapolation yields a very large amount of the subhalo boost factor of ≳100 for galaxy-size halos. Physically motivated theoretical models based on analytic prescriptions such as the extended Press-Schechter formalism and tidal stripping modeling, which are well tested against the simulation results, predict a more modest boost of order unity for the galaxy-size halos. Giving an accurate assessment of the boost factor is essential for indirect dark matter searches and thus, having models calibrated at large ranges of host masses and redshifts, is strongly urged upon.

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Concentration, ellipsoidal collapse, and the densest dark matter haloes

Cited by 42 publications

References 44 publications

Halo Profiles and the Concentration–Mass Relation for a ΛCDM Universe

Halo Profiles and the Concentration–Mass Relation for a ΛCDM Universe

An Accurate Physical Model for Halo Concentrations

Halo Substructure Boosts to the Signatures of Dark Matter Annihilation

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