scholarly journals How biased are halo properties in cosmological simulations?

2020 ◽  
Vol 500 (3) ◽  
pp. 3309-3328
Author(s):  
Philip Mansfield ◽  
Camille Avestruz
Keyword(s):  
Dark Matter ◽  
Empirical Model ◽  
Empirical Models ◽  
Rotation Curves ◽  
Cosmological Simulations ◽  
Wide Range ◽  
Practical Convergence ◽  
Halo Population ◽  
The Impact

ABSTRACT Cosmological N-body simulations have been a major tool of theorists for decades, yet many of the numerical issues that these simulations face are still unexplored. This paper measures numerical biases in these large, dark matter-only simulations that affect the properties of their dark matter haloes. We compare many simulation suites in order to provide several tools for simulators and analysts which help mitigate these biases. We summarize our comparisons with practical ‘convergence limits’ that can be applied to a wide range of halo properties, including halo properties which are traditionally overlooked by the testing literature. We also find that the halo properties predicted by different simulations can diverge from one another at unexpectedly high resolutions. We demonstrate that many halo properties depend strongly on force softening scale and that this dependence leads to much of the measured divergence between simulations. We offer an empirical model to estimate the impact of such effects on the rotation curves of a halo population. This model can serve as a template for future empirical models of the biases in other halo properties.

scholarly journals Numerical convergence of simulations of galaxy formation: the abundance and internal structure of cold dark matter haloes

2019 ◽  
Vol 488 (3) ◽  
pp. 3663-3684 ◽  
Author(s):  
Aaron D Ludlow ◽  
Joop Schaye ◽  
Richard Bower
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Particle Number ◽  
Velocity Profiles ◽  
Scaling Relations ◽  
Cosmological Simulations ◽  
Particle Spacing ◽  
Circular Velocity ◽  
Wide Range ◽  
The Impact

ABSTRACT We study the impact of numerical parameters on the properties of cold dark matter haloes formed in collisionless cosmological simulations. We quantify convergence in the median spherically averaged circular velocity profiles for haloes of widely varying particle number, as well as in the statistics of their structural scaling relations and mass functions. In agreement with prior work focused on single haloes, our results suggest that cosmological simulations yield robust halo properties for a wide range of gravitational softening parameters, ϵ, provided: (1) ϵ is not larger than a ‘convergence radius’, rconv, which is dictated by two-body relaxation and determined by particle number, and (2) a sufficient number of time-steps are taken to accurately resolve particle orbits with short dynamical times. Provided these conditions are met, median circular velocity profiles converge to within ≈10 per cent for radii beyond which the local two-body relaxation time-scale exceeds the Hubble time by a factor $\kappa \equiv t_{\rm relax}/t_{\rm H}\rm{\,\, \buildrel\gt \over \sim \,\,}0.177$, with better convergence attained for higher κ. We provide analytic estimates of rconv that build on previous attempts in two ways: first, by highlighting its explicit (but weak) softening-dependence and, second, by providing a simpler criterion in which rconv is determined entirely by the mean inter-particle spacing, l, for example better than 10 per cent convergence in circular velocity for $r\rm{\,\, \buildrel\gt \over \sim \,\,}0.05\, l$. We show how these analytic criteria can be used to assess convergence in structural scaling relations for dark matter haloes as a function of their mass or maximum circular speed.

scholarly journals Energy equipartition between stellar and dark matter particles in cosmological simulations results in spurious growth of galaxy sizes

2019 ◽  
Vol 488 (1) ◽  
pp. L123-L128 ◽  
Author(s):  
Aaron D Ludlow ◽  
Joop Schaye ◽  
Matthieu Schaller ◽  
Jack Richings
Keyword(s):  
Dark Matter ◽  
Dark Matter Particle ◽  
Mass Resolution ◽  
Particle Mass ◽  
Cosmological Simulations ◽  
Massive Particles ◽  
Energy Equipartition ◽  
Mass Segregation ◽  
Baryonic Mass ◽  
The Impact

ABSTRACTThe impact of 2-body scattering on the innermost density profiles of dark matter haloes is well established. We use a suite of cosmological simulations and idealized numerical experiments to show that 2-body scattering is exacerbated in situations where there are two species of unequal mass. This is a consequence of mass segregation and reflects a flow of kinetic energy from the more to less massive particles. This has important implications for the interpretation of galaxy sizes in cosmological hydrodynamic simulations, which nearly always model stars with less massive particles than are used for the dark matter. We compare idealized models as well as simulations from the eagle project that differ only in the mass resolution of the dark matter component, but keep subgrid physics, baryonic mass resolution, and gravitational force softening fixed. If the dark matter particle mass exceeds the mass of stellar particles, then galaxy sizes – quantified by their projected half-mass radii, R50 – increase systematically with time until R50 exceeds a small fraction of the redshift-dependent mean interparticle separation, l (${\rm R_{50}} \gtrsim 0.05\times l$). Our conclusions should also apply to simulations that adopt different hydrodynamic solvers, subgrid physics, or adaptive softening, but in that case may need quantitative revision. Any simulation employing a stellar-to-dark matter particle mass ratio greater than unity will escalate spurious energy transfer from dark matter to baryons on small scales.

scholarly journals Mixed dark matter: matter power spectrum and halo mass function

2021 ◽  
Vol 2021 (12) ◽  
pp. 044
Author(s):  
G. Parimbelli ◽  
G. Scelfo ◽  
S.K. Giri ◽  
A. Schneider ◽  
M. Archidiacono ◽  
...  
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Large Scale ◽  
Cosmological Parameters ◽  
Mass Function ◽  
Large Set ◽  
Cluster Number ◽  
Matter Power Spectrum ◽  
Wide Range ◽  
The Impact

Abstract We investigate and quantify the impact of mixed (cold and warm) dark matter models on large-scale structure observables. In this scenario, dark matter comes in two phases, a cold one (CDM) and a warm one (WDM): the presence of the latter causes a suppression in the matter power spectrum which is allowed by current constraints and may be detected in present-day and upcoming surveys. We run a large set of N-body simulations in order to build an efficient and accurate emulator to predict the aforementioned suppression with percent precision over a wide range of values for the WDM mass, Mwdm, and its fraction with respect to the totality of dark matter, fwdm. The suppression in the matter power spectrum is found to be independent of changes in the cosmological parameters at the 2% level for k≲ 10 h/Mpc and z≤ 3.5. In the same ranges, by applying a baryonification procedure on both ΛCDM and CWDM simulations to account for the effect of feedback, we find a similar level of agreement between the two scenarios. We examine the impact that such suppression has on weak lensing and angular galaxy clustering power spectra. Finally, we discuss the impact of mixed dark matter on the shape of the halo mass function and which analytical prescription yields the best agreement with simulations. We provide the reader with an application to galaxy cluster number counts.

scholarly journals Dark Matter Halos: The Dynamical Basis of Effective Empirical Models

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
Andrea Lapi ◽  
Alfonso Cavaliere
Keyword(s):  
Dark Matter ◽  
Boundary Conditions ◽  
Empirical Models ◽  
Small Scale ◽  
Dark Matter Halos ◽  
Close Approximation ◽  
Dynamical Models ◽  
Dynamical Equilibrium ◽  
The Impact ◽  
Physical Boundary

We investigate the dynamical basis of the classic empirical models (specifically, Sérsic-Einasto and generalized NFW) that are widely used to describe the distributions of collisionless matter in galaxies. We submit that such a basis is provided by ourα-profiles, shown to constitute solutions of the Jeans dynamical equilibrium with physical boundary conditions. We show how to set the parameters of the empirical in terms of the dynamical models; we find the empirical models, and specifically Sérsic-Einasto, to constitute a simple and close approximation to the dynamical models. Finally, we discuss how these provide a useful baseline for assessing the impact of the small-scale dynamics that may modulate the density slope in the central galaxy regions.

scholarly journals Inner Halo Shapes of Dwarf Galaxies: Resolving the Cusp/Core Problem

2004 ◽  
Vol 220 ◽  
pp. 371-372 ◽  
Author(s):  
Kristine Spekkens ◽  
Riccardo Giovanelli
Keyword(s):  
Dark Matter ◽  
Data Processing ◽  
Density Profile ◽  
Dwarf Galaxies ◽  
Dark Matter Halo ◽  
High Quality ◽  
Rotation Curves ◽  
Processing Errors ◽  
The Impact ◽  
Core Problem

We derive inner dark matter halo density profile slopes for a sample of 200 dwarf galaxies by inverting rotation curves obtained from high-quality, long-slit optical spectra. Using simulations to assess the impact of long-slit observing and data processing errors on our measurements, we conclude that our observations are consistent with the cuspy halos predicted by the CDM paradigm.

scholarly journals Neutrino interactions in the late universe

2021 ◽  
Vol 2021 (11) ◽  
Author(s):  
Daniel Green ◽  
David E. Kaplan ◽  
Surjeet Rajendran
Keyword(s):  
Dark Matter ◽  
Big Bang ◽  
Late Time ◽  
Beyond The Standard Model ◽  
Neutrino Sector ◽  
Cosmic Neutrino Background ◽  
Wide Range ◽  
Cosmic Neutrino ◽  
Near Term ◽  
The Impact

Abstract The cosmic neutrino background is both a dramatic prediction of the hot Big Bang and a compelling target for current and future observations. The impact of relativistic neutrinos in the early universe has been observed at high significance in a number of cosmological probes. In addition, the non-zero mass of neutrinos alters the growth of structure at late times, and this signature is a target for a number of upcoming surveys. These measurements are sensitive to the physics of the neutrino and could be used to probe physics beyond the standard model in the neutrino sector. We explore an intriguing possibility where light right-handed neutrinos are coupled to all, or a fraction of, the dark matter through a mediator. In a wide range of parameter space, this interaction only becomes important at late times and is uniquely probed by late-time cosmological observables. Due to this coupling, the dark matter and neutrinos behave as a single fluid with a non-trivial sound speed, leading to a suppression of power on small scales. In current and near-term cosmological surveys, this signature is equivalent to an increase in the sum of the neutrino masses. Given current limits, we show that at most 0.5% of the dark matter could be coupled to neutrinos in this way.

scholarly journals A black box for dark sector physics: predicting dark matter annihilation feedback with conditional GANs

2019 ◽  
Vol 490 (3) ◽  
pp. 3134-3143 ◽  
Author(s):  
Florian List ◽  
Ishaan Bhat ◽  
Geraint F Lewis
Keyword(s):  
Dark Matter ◽  
Generative Adversarial Networks ◽  
Dark Sector ◽  
Dark Matter Annihilation ◽  
Average Deviation ◽  
Simulation Code ◽  
Cosmological Simulations ◽  
Gas Density ◽  
Adversarial Networks ◽  
The Impact

Abstract Traditionally, incorporating additional physics into existing cosmological simulations requires re-running the cosmological simulation code, which can be computationally expensive. We show that conditional Generative Adversarial Networks (cGANs) can be harnessed to predict how changing the underlying physics alters the simulation results. To illustrate this, we train a cGAN to learn the impact of dark matter annihilation feedback (DMAF) on the gas density distribution. The predicted gas density slices are visually difficult to distinguish from their real brethren and the peak counts differ by less than 10 per cent for all test samples (the average deviation is <3 per cent). Finally, we invert the problem and show that cGANs are capable of endowing smooth density distributions with realistic substructure. The cGAN does however have difficulty generating new knots as well as creating/eliminating bubble-like structures. We conclude that trained cGANs can be an effective approach to provide mock samples of cosmological simulations incorporating DMAF physics from existing samples of standard cosmological simulations of the evolution of cosmic structure.

scholarly journals Baryons Shaping Dark Matter Haloes

2020 ◽  
Author(s):  
P Cataldi ◽  
S E Pedrosa ◽  
P B Tissera ◽  
M C Artale
Keyword(s):  
Dark Matter ◽  
Mass Range ◽  
Orbital Structure ◽  
Intrinsic Properties ◽  
Cosmological Simulations ◽  
Velocity Anisotropy ◽  
Relative Decrease ◽  
Central Regions ◽  
The Impact ◽  
Disc Galaxies

Abstract In this work we aim at investigating the effects of baryons on the dark matter (DM) haloes structure, focusing on the correlation between the presence and importance of stellar discs and the halo shapes. We study the properties of a subsample of DM haloes from Fenix and eagle cosmological simulations. We inspect the central regions of haloes in the mass range $[10.9-992.3] \times 10^{10} \ \rm M_{\odot }$ at z = 0, comparing the hydrodynamic runs and their dark matter only (DMo) counterparts. Our results indicate that baryons have a significant impact on the shape of the inner halo, mainly within ∼ 20 percent of the virial radius. We find haloes to be more spherical when hosting baryons. While the impact of baryons depends on the mass of the haloes, we also find a trend with morphology which suggests that the way baryons are assembled is also relevant in agreement with previous works. Our findings also indicate that disc galaxies preferentially form in haloes whose DMo counterparts were originally more spherical and with stronger velocity anisotropy. The presence of baryons alter the orbital structure of the DM particles of the haloes, which show a decrease in their velocity anisotropy, towards more tangentially biased orbits. This relative decrease is weaker in the case of disc-dominated galaxies. Our results point out to a cosmological connection between the final morphology of galaxies and the intrinsic properties of their DM haloes, which gets reinforce by the growth of the discs.

scholarly journals The impact of baryonic physics on the structure of dark matter haloes: the view from the FIRE cosmological simulations

2015 ◽  
Vol 454 (3) ◽  
pp. 2981-3001 ◽  
Author(s):  
T. K. Chan ◽  
D. Kereš ◽  
J. Oñorbe ◽  
P. F. Hopkins ◽  
A. L. Muratov ◽  
...  
Keyword(s):  
Dark Matter ◽  
Cosmological Simulations ◽  
The Impact
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