Confrontation of top-hat spherical collapse against dark halos from cosmological <i>N</i>-body simulations

Suto, Daichi; Kitayama, Tetsu; Osato, Ken; Sasaki, Shin; Suto, Yasushi

doi:10.1093/pasj/psv122

Cited by 12 publications

(9 citation statements)

References 46 publications

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“…The NFW halo is assumed to be radially symmetric and requires truncation at a finite radius in order to prevent the integrated mass diverging as r → ∞. The truncation is typically set by the virial radius, which is itself determined approximately via the spherical top-hat collapse model describing the evolution of a uniform spherical overdensity in a smooth expanding background (White 2001;Suto et al 2016;Herrera, Waga, & Jorás 2017). Gravitational collapse of the overdensity halts when virial equilibrium is reached.…”

Section: Semi-analytic Halosmentioning

confidence: 99%

The core-cusp problem revisited: ULDM vs. CDM

Kendall

Easther

2020

Publ. Astron. Soc. Aust.

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The core-cusp problem is often cited as a motivation for the exploration of dark matter models beyond standard CDM [cold dark matter]. One such alternative is ULDM [ultra-light dark matter]; particles exhibiting wavelike properties on kiloparsec scales. ULDM dynamics are governed by the Schrödinger-Poisson equations, which have solitonic ground state solutions consisting of gravitationally-bound condensates with no internal kinetic energy. Astrophysically realistic ULDM halos would consist of larger NFW-like configurations with a possible solitonic core. We describe a parameterisation for the radial density profiles of ULDM halos that accounts for the environmental variability of the core-halo mass relation. We then compare the semi-analytic profiles of ULDM and CDM with astrophysical data, and find that a ULDM particle mass of 10 −23 eV can yield a reasonably good fit to observed rotation data, particularly at small radii. This ULDM mass is in tension with other constraints but we note that this analysis ignores any contribution from baryonic feedback.It is widely agreed that non-baryonic dark matter constitutes the majority of the mass of the observable universe, but its precise nature remains an open question. Many dark matter models have been proposed, with particle CDM [Cold Dark Matter] being the most widely studied. This scenario successfully accounts for the large scale structure of the universe [1] and the spectrum of anisotropies in the microwave background [2-8], but the so-called "smallscale crisis" remains a challenge [9]. A key issue is the tension between the central density profiles of dark matter halos in simulations containing only gravitationally interacting CDM, and those inferred from observational data. Simulations tend to produce 'cuspy' central density profiles [10], which grow as 1/r at small radii, but observational data appears to favour flattened central cores [11]. This so-called core-cusp problem has been the focus of much recent attention [12][13][14].The seriousness of the core-cusp problem is the subject of ongoing debate, and may be ameliorated by adding baryonic matter to CDM simulations [15]. Nevertheless, the wider category of "small-scale" problems in standard CDM along with tighter constraints from direct-detection experiments [16] motivates the study of alternative dark matter models. One scenario which has gained substantial traction is ultra-light dark matter [ULDM], also known as scalar-field dark matter, Ψ dark matter, axion dark matter, BEC dark matter and fuzzy dark matter. As reviewed by Hui et al. [17], ULDM consists of an axion-like particle whose very small mass (O(∼ 10 −22 eV )) corresponds to a kiloparsec-scale de Broglie wavelength. ULDM thus exhibits novel wave-like behaviour on astrophysically interesting scales and can form soliton-like gravitationally confined Bose-Einstein condensates. ULDM simulations suggest that realistic astrophysical halos have an inner core consisting of a kiloparsec scale Bose-Einstein condensate or soliton, while the outer halo is ...

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Section: Semi-analytic Halosmentioning

confidence: 99%

The core-cusp problem revisited: ULDM vs. CDM

Kendall

Easther

2020

Publ. Astron. Soc. Aust.

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“…Actually, the difference between the model prediction and the simulation results is not peculiar to EC. In Suto et al (2016), we compare the evolution of the spherical radius of individual simulated halos with the prediction of the spherical collapse model. We then showed that the spherical collapse model fairly well reproduce the evolution of the simulation results up to the turn-around epoch.…”

Section: Comparison Of Evolution Of Individual Halos With Ec Predictionmentioning

confidence: 99%

Evolution and statistics of non-sphericity of dark matter halos from cosmological N-body simulation

Suto

Kitayama

Nishimichi

et al. 2016

Publications of the Astronomical Society of Japan

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We revisit the non-sphericity of cluster-mass scale halos from cosmological N-body simulation on the basis of triaxial modelling. In order to understand the difference between the simulation results and the conventional ellipsoidal collapse model (EC), we first consider the evolution of individual simulated halos. The major difference between EC and the simulation becomes appreciable after the turn-around epoch. Moreover, it is sensitive to the individual evolution history of each halo. Despite such strong dependence on individual halos, the resulting nonsphericity of halos exhibits weak but robust mass dependence in a statistical fashion; massive halos are more spherical up to the turn-around, but gradually become less spherical by z = 0. This is clearly inconsistent with the EC prediction; massive halos are usually more spherical. In 1 addition, at z = 0, inner regions of the simulated halos are less spherical than outer regions, i.e., the density distribution inside the halos is highly inhomogeneous and therefore not self-similar (concentric ellipsoids with the same axis ratio and orientation). This is also inconsistent with the homogeneous density distribution that is commonly assumed in EC. Since most of previous fitting formulae for the probability distribution function (PDF) of axis ratio of triaxial ellipsoids have been constructed under the self-similarity assumption, they are not accurate. Indeed, we compute the PDF of projected axis ratio a 1 /a 2 directly from the simulation data without the self-similarity assumption, and find that it is very sensitive to the assumption. The latter needs to be carefully taken into account in direct comparison with observations, and therefore we provide an empirical fitting formula for the PDF of a 1 /a 2 . Our preliminary analysis suggests that the derived PDF of a 1 /a 2 roughly agrees with the current weak-lensing observations. More importantly, the present results will be useful in future exploration of the non-sphericity of clusters in X-ray and optical observations.

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“…This suggests that the self-similar solution may capture the overall trends in the dynamics of accreting material on to CDM halos in simulations, and possibly those in the real universe if the CDM scenario is true, although it is very hard to imagine that spherically symmetric and isolated halo is realized in reality. In fact, even when starting from a nearly spherically symmetric initial condition, non-sphericity is rapidly developed due to the so-called radial-orbit instability (e.g., Binney & Tremaine 2008), and a deviation from the top-hat spherical collapse model is significant (Suto et al 2016a). The resultant halo exhibits an elongated triaxial shape (e.g., Jing & Suto 2002;Suto et al 2016b), rather different from the prediction of the self-similar solution (e.g., MacMillan et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Phase-space structure of cold dark matter haloes inside splashback: multistream flows and self-similar solution

Sugiura

Nishimichi

Taruya

2020

Monthly Notices of the Royal Astronomical Society

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Using the motion of accreting particles onto halos in cosmological N-body simulations, we study the radial phase-space structures of cold dark matter (CDM) halos. In CDM cosmology, formation of virialized halos generically produces radial caustics, followed by multi-stream flows of accreted dark matter inside the halos, which are clues to discriminate from non-standard dark matter models. In particular, the radius of the outermost caustic called the splashback radius exhibits a sharp drop in the slope of the density profile, and is recognized with great interest as a physical boundary of CDM halos in both theory and observation. Here, we focus on the multi-stream structure of CDM halos inside the splashback radius. To analyze this, we created an algorithm based on the SPARTA algorithm developed by Diemer (2017), and by tracking the particle trajectories accreting onto the halos, we count their number of apocenter passages, which is then used to reveal the multi-stream flows of the dark matter particles. The resultant multi-stream structure in radial phase space is then compared with the prediction of the self-similar solution by Fillmore & Goldreich (1984) for each halo. We find that ∼ 30% of the simulated halos satisfy our criteria to be regarded as being well fitted to the self-similar solution. The fitting parameters in the self-similar solution characterizes physical properties of the halos, including the mass accretion rate and the size of the outermost caustic (i.e., the splashback radius). We discuss in detail the correlation of these fitting parameters and other measures directly extracted from the N-body simulation.

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Confrontation of top-hat spherical collapse against dark halos from cosmological N-body simulations

Cited by 12 publications

References 46 publications

The core-cusp problem revisited: ULDM vs. CDM

The core-cusp problem revisited: ULDM vs. CDM

Evolution and statistics of non-sphericity of dark matter halos from cosmological N-body simulation

Phase-space structure of cold dark matter haloes inside splashback: multistream flows and self-similar solution

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