scholarly journals On N-body simulations of globular cluster streams

2021 ◽  
Vol 504 (1) ◽  
pp. 648-653
Author(s):  
Nilanjan Banik ◽  
Jo Bovy
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Analytical Models ◽  
Numerical Density ◽  
Stellar Streams ◽  
Small Scales ◽  
Order Of Magnitude ◽  
Low Mass ◽  
Stream Density ◽  
Tidal Streams

ABSTRACT Stellar tidal streams are sensitive tracers of the properties of the gravitational potential in which they orbit and detailed observations of their density structure can be used to place stringent constraints on fluctuations in the potential caused by, e.g. the expected populations of dark matter subhaloes in the standard cold dark matter (CDM) paradigm. Simulations of the evolution of stellar streams in live N-body haloes without low-mass dark matter subhaloes, however, indicate that streams exhibit significant perturbations on small scales even in the absence of substructure. Here, we demonstrate, using high-resolution N-body simulations combined with sophisticated semi-analytical and simple analytical models, that the mass resolutions of 104–$10^5\, \rm {M}_{\odot }$ commonly used to perform such simulations cause spurious stream density variations with a similar magnitude on large scales as those expected from a CDM-like subhalo population and an order of magnitude larger on small, yet observable, scales. We estimate that mass resolutions of ${\approx}100\, \rm {M}_{\odot }$ (${\approx}1\, \rm {M}_{\odot }$) are necessary for spurious, numerical density variations to be well below the CDM subhalo expectation on large (small) scales. That streams are sensitive to a simulation’s particle mass down to such small masses indicates that streams are sensitive to dark matter clustering down to these low masses if a significant fraction of the dark matter is clustered or concentrated in this way, for example, in MACHO models with masses of 10–$100\, \rm {M}_{\odot }$.

scholarly journals Impact of dark matter models on the EoR 21-cm signal bispectrum

2020 ◽  
Vol 497 (3) ◽  
pp. 2941-2953 ◽  
Author(s):  
Anchal Saxena ◽  
Suman Majumdar ◽  
Mohd Kamran ◽  
Matteo Viel
Keyword(s):  
Dark Matter ◽  
Structure Formation ◽  
Cold Dark Matter ◽  
Power Spectra ◽  
Neutral Hydrogen ◽  
Cosmic Time ◽  
Lower Number ◽  
Neutral Fraction ◽  
Small Scales ◽  
Low Mass

ABSTRACT The nature of dark matter sets the timeline for the formation of first collapsed haloes and thus affects the sources of reionization. Here, we consider two different models of dark matter: cold dark matter (CDM) and thermal warm dark matter (WDM), and study how they impact the epoch of reionization (EoR) and its 21-cm observables. Using a suite of simulations, we find that in WDM scenarios, the structure formation on small scales gets suppressed, resulting in a smaller number of low-mass dark matter haloes compared to the CDM scenario. Assuming that the efficiency of sources in producing ionizing photons remains the same, this leads to a lower number of total ionizing photons produced at any given cosmic time, thus causing a delay in the reionization process. We also find visual differences in the neutral hydrogen (H i) topology and in 21-cm maps in case of the WDM compared to the CDM. However, differences in the 21-cm power spectra, at the same neutral fraction, are found to be small. Thus, we focus on the non-Gaussianity in the EoR 21-cm signal, quantified through its bispectrum. We find that the 21-cm bispectra (driven by the H i topology) are significantly different in WDM models compared to the CDM, even for the same mass-averaged neutral fractions. This establishes that the 21-cm bispectrum is a unique and promising way to differentiate between dark matter models, and can be used to constrain the nature of the dark matter in the future EoR observations.

scholarly journals Dwarf Galaxies as Cosmological Probes

2018 ◽  
Vol 14 (S344) ◽  
pp. 455-463
Author(s):  
Julio F. Navarro
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Dark Matter Halos ◽  
Too Big To Fail ◽  
Sharp Minimum ◽  
Luminous Galaxies ◽  
Small Scales ◽  
Low Mass

AbstractThe Lambda Cold Dark Matter (LCDM) paradigm makes specific predictions for the abundance, structure, substructure and clustering of dark matter halos, the sites of galaxy formation. These predictions can be directly tested, in the low-mass halo regime, by dark matter-dominated dwarf galaxies. A number of potential challenges to LCDM have been identified when confronting the expected properties of dwarfs with observation. I review our understanding of a few of these issues, including the “missing satellites” and the “too-big-to-fail” problems, and argue that neither poses an insurmountable challenge to LCDM. Solving these problems requires that most dwarf galaxies inhabit halos of similar mass, and that there is a relatively sharp minimum halo mass threshold to form luminous galaxies. These predictions are eminently falsifiable. In particular, LCDM predicts a large number of “dark” low-mass halos, some of which should have retained enough primordial gas to be detectable in deep 21 cm or Hα surveys. Detecting this predicted population of “mini-halos” would be a major discovery and a resounding success for LCDM on small scales.

scholarly journals Probing the nature of dark matter with accreted globular cluster streams

2020 ◽  
Vol 501 (1) ◽  
pp. 179-200 ◽  
Author(s):  
Khyati Malhan ◽  
Monica Valluri ◽  
Katherine Freese
Keyword(s):  
Dark Matter ◽  
Globular Cluster ◽  
Particle Physics ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Density Profiles ◽  
Parallel Structures ◽  
Stellar Streams ◽  
Future Data ◽  
Low Mass

ABSTRACT The steepness of the central density profiles of dark matter (DM) in low-mass galaxy haloes (e.g. dwarf galaxies) is a powerful probe of the nature of DM. We propose a novel scheme to probe the inner profiles of galaxy subhaloes using stellar streams. We show that the present-day morphological and dynamical properties of accreted globular cluster (GC) streams – those produced from tidal stripping of GCs that initially evolved within satellite galaxies and later merged with the Milky Way (MW) – are sensitive to the central DM density profile and mass of their parent satellites. GCs that accrete within cuspy cold dark matter (CDM) subhaloes produce streams that are physically wider and dynamically hotter than streams that accrete inside cored subhaloes. A first comparison of MW streams ‘GD-1’ and ‘Jhelum’ (likely of accreted GC origin) with our simulations indicates a preference for cored subhaloes. If these results hold up in future data, the implication is that either the DM cusps were erased by baryonic feedback, or their subhaloes naturally possessed cored density profiles implying particle physics models beyond CDM. Moreover, accreted GC streams are highly structured and exhibit complex morphological features (e.g. parallel structures and ‘spurs’). This implies that the accretion scenario can naturally explain the recently observed peculiarities in some of the MW streams. We also propose a novel mechanism for forming ‘gaps’ in stellar streams when the remnant of the parent subhalo (which hosted the GC) later passes through the GC stream. This encounter can last a longer time (and have more of an impact) than the random encounters with DM subhaloes previously considered, because the GC stream and its parent subhalo are on similar orbits with small relative velocities. Current and future surveys of the MW halo will uncover numerous faint stellar streams and provide the data needed to substantiate our preliminary tests with this new probe of DM.

scholarly journals Galaxy clusters in the context of superfluid dark matter

2017 ◽  
Vol 607 ◽  
pp. A108 ◽  
Author(s):  
Alistair O. Hodson ◽  
Hongsheng Zhao ◽  
Justin Khoury ◽  
Benoit Famaey
Keyword(s):  
Dark Matter ◽  
Galaxy Clusters ◽  
Cold Dark Matter ◽  
Mass Scale ◽  
Normal Phase ◽  
Dark Halo ◽  
Small Scales ◽  
Order Of Magnitude ◽  
Superfluid Core ◽  
Two Parameters

Context. The mass discrepancy in the Universe has not been solved by the cold dark matter (CDM) or the modified Newtonian dynamics (MOND) paradigms so far. The problems and solutions of either scenario are mutually exclusive on large and small scales. It has recently been proposed, by assuming that dark matter is a superfluid, that MOND-like effects can be achieved on small scales whilst preserving the success of ΛCDM on large scales. Detailed models within this “superfluid dark matter” (SfDM) paradigm are yet to be constructed. Aims. Here, we aim to provide the first set of spherical models of galaxy clusters in the context of SfDM. We aim to determine whether the superfluid formulation is indeed sufficient to explain the mass discrepancy in galaxy clusters. Methods. The SfDM model is defined by two parameters. Λ can be thought of as a mass scale in the Lagrangian of the scalar field that effectively describes the phonons, and it acts as a coupling constant between the phonons and baryons. m is the mass of the DM particles. Based on these parameters, we outline the theoretical structure of the superfluid core and the surrounding “normal-phase” dark halo of quasi-particles. The latter are thought to encompass the largest part of galaxy clusters. Here, we set the SfDM transition at the radius where the density and pressure of the superfluid and normal phase coincide, neglecting the effect of phonons in the superfluid core. We then apply the formalism to a sample of galaxy clusters, and directly compare the SfDM predicted mass profiles to data. Results. We find that the superfluid formulation can reproduce the X-ray dynamical mass profile of clusters reasonably well, but with a slight under-prediction of the gravity in the central regions. This might be partly related to our neglecting of the effect of phonons in these regions. Two normal-phase halo profiles are tested, and it is found that clusters are better defined by a normal-phase halo resembling an Navarro-Frenk-White-like structure than an isothermal profile. Conclusions. In this first exploratory work on the topic, we conclude that depending on the amount of baryons present in the central galaxy and on the actual effect of phonons in the inner regions, this superfluid formulation could be successful in describing galaxy clusters. In the future, our model could be made more realistic by exploring non-sphericity and a more realistic SfDM to normal phase transition. The main result of this study is an estimate of the order of magnitude of the theory parameters for the superfluid formalism to be reasonably consistent with clusters. These values will have to be compared to the true values needed in galaxies.

scholarly journals Halo concentration strengthens dark matter constraints in galaxy-galaxy strong lensing analyses

2021 ◽  
Author(s):  
Nicola C Amorisco ◽  
James Nightingale ◽  
Qiuhan He ◽  
Aristeidis Amvrosiadis ◽  
Xiaoyue Cao ◽  
...  
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Large Population ◽  
Dark Matter Particle ◽  
Mass Function ◽  
Gravitational Lenses ◽  
High Concentration ◽  
Expected Number ◽  
Order Of Magnitude ◽  
Low Mass

Abstract A defining prediction of the cold dark matter (CDM) cosmological model is the existence of a very large population of low-mass haloes. This population is absent in models in which the dark matter particle is warm (WDM). These alternatives can, in principle, be distinguished observationally because halos along the line-of-sight can perturb galaxy-galaxy strong gravitational lenses. Furthermore, the WDM particle mass could be deduced because the cut-off in their halo mass function depends on the mass of the particle. We systematically explore the detectability of low-mass haloes in WDM models by simulating and fitting mock lensed images. Contrary to previous studies, we find that halos are harder to detect when they are either behind or in front of the lens. Furthermore, we find that the perturbing effect of haloes increases with their concentration: detectable haloes are systematically high-concentration haloes, and accounting for the scatter in the mass-concentration relation boosts the expected number of detections by as much as an order of magnitude. Haloes have lower concentration for lower particle masses and this further suppresses the number of detectable haloes beyond the reduction arising from the lower halo abundances alone. Taking these effects into account can make lensing constraints on the value of the mass function cut-off at least an order of magnitude more stringent than previously appreciated.

scholarly journals Understanding the large inferred Einstein radii of observed low-mass galaxy clusters

2020 ◽  
Vol 494 (4) ◽  
pp. 4706-4712 ◽  
Author(s):  
Andrew Robertson ◽  
Richard Massey ◽  
Vincent Eke
Keyword(s):  
Dark Matter ◽  
Galaxy Clusters ◽  
Gravitational Lensing ◽  
Cold Dark Matter ◽  
Baryonic Matter ◽  
Analysis Method ◽  
Critical Curves ◽  
Hydrodynamical Simulation ◽  
Low Mass ◽  
Main Effects

ABSTRACT We assess a claim that observed galaxy clusters with mass ${\sim}10^{14} \mathrm{\, M_\odot }$ are more centrally concentrated than predicted in lambda cold dark matter (ΛCDM). We generate mock strong gravitational lensing observations, taking the lenses from a cosmological hydrodynamical simulation, and analyse them in the same way as the real Universe. The observed and simulated lensing arcs are consistent with one another, with three main effects responsible for the previously claimed inconsistency. First, galaxy clusters containing baryonic matter have higher central densities than their counterparts simulated with only dark matter. Secondly, a sample of clusters selected because of the presence of pronounced gravitational lensing arcs preferentially finds centrally concentrated clusters with large Einstein radii. Thirdly, lensed arcs are usually straighter than critical curves, and the chosen image analysis method (fitting circles through the arcs) overestimates the Einstein radii. After accounting for these three effects, ΛCDM predicts that galaxy clusters should produce giant lensing arcs that match those in the observed Universe.

scholarly journals Structure of Dark Matter Halo

1999 ◽  
Vol 183 ◽  
pp. 155-155
Author(s):  
Toshiyuki Fukushige ◽  
Junichiro Makino
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Temperature Inversion ◽  
Dark Matter Halo ◽  
Temperature Structure ◽  
Galactic Halos ◽  
Dark Matter Halos ◽  
Density Profiles ◽  
Order Of Magnitude ◽  
Special Purpose Computer

We performed N-body simulation on special-purpose computer, GRAPE-4, to investigate the structure of dark matter halos (Fukushige, T. and Makino, J. 1997, ApJL, 477, L9). Universal profile proposed by Navarro, Frenk, and White (1996, ApJ, 462, 563), which has cusp with density profiles ρ ∝r−1in density profile, cannot be reproduced in the standard Cold Dark Matter (CDM) picture of hierarchical clustering. Previous claims to the contrary were based on simulations with relatively few particles, and substantial softening. We performed simulations with particle numbers an order of magnitude higher, and essentially no softening, and found that typical central density profiles are clearly steeper than ρ ∝r−1, as shown in Figure 1. In addition, we confirm the presence of a temperature inversion in the inner 5 kpc of massive galactic halos, and give a natural explanation for formation of the temperature structure.

The Expected Mass Function for Low‐Mass Galaxies in a Cold Dark Matter Cosmology: Is There a Problem?

2001 ◽  
Vol 563 (1) ◽  
pp. 21-27 ◽  
Author(s):  
Weihsueh A. Chiu ◽  
Nickolay Y. Gnedin ◽  
Jeremiah P. Ostriker
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Mass Function ◽  
Low Mass

scholarly journals Predictably missing satellites: subhalo abundances in Milky Way-like haloes

2019 ◽  
Vol 486 (4) ◽  
pp. 4545-4568 ◽  
Author(s):  
Catherine E Fielder ◽  
Yao-Yuan Mao ◽  
Jeffrey A Newman ◽  
Andrew R Zentner ◽  
Timothy C Licquia
Keyword(s):  
Dark Matter ◽  
Confidence Level ◽  
Mass Concentration ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Scale Factor ◽  
Magellanic Clouds ◽  
Small Scales ◽  
Major Merger ◽  
The Impact

ABSTRACT On small scales there have been a number of claims of discrepancies between the standard cold dark matter (CDM) model and observations. The ‘missing satellites problem’ infamously describes the overabundance of subhaloes from CDM simulations compared to the number of satellites observed in the Milky Way. A variety of solutions to this discrepancy have been proposed; however, the impact of the specific properties of the Milky Way halo relative to the typical halo of its mass has yet to be explored. Motivated by recent studies that identified ways in which the Milky Way is atypical, we investigate how the properties of dark matter haloes with mass comparable to our Galaxy’s – including concentration, spin, shape, and scale factor of the last major merger – correlate with the subhalo abundance. Using zoom-in simulations of Milky Way-like haloes, we build two models of subhalo abundance as functions of host halo properties. From these models we conclude that the Milky Way most likely has fewer subhaloes than the average halo of the same mass. We expect up to 30 per cent fewer subhaloes with low maximum rotation velocities ($V_{\rm max}^{\rm sat} \sim 10$ km s−1) at the 68 per cent confidence level and up to 52 per cent fewer than average subhaloes with high rotation velocities ($V_{\rm max}^{\rm sat} \gtrsim 30$ km s−1, comparable to the Magellanic Clouds) than would be expected for a typical halo of the Milky Way’s mass. Concentration is the most informative single parameter for predicting subhalo abundance. Our results imply that models tuned to explain the missing satellites problem assuming typical subhalo abundances for our Galaxy may be overcorrecting.

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