Halo Structure Research Articles

Cosmological simulations of two-component wave dark matter

ABSTRACT Wave (fuzzy) dark matter ($\psi \rm {DM}$) consists of ultralight bosons, featuring a solitonic core within a granular halo. Here we extend $\psi \rm {DM}$ to two components, with distinct particle masses m and coupled only through gravity, and investigate the resulting soliton–halo structure via cosmological simulations. Specifically, we assume $\psi \rm {DM}$ contains 75 per cent major component and 25 per cent minor component, fix the major-component particle mass to $m_{\rm major}=1\times 10^{-22}\, \rm eV$, and explore two different minor-component particle masses with mmajor: mminor = 3: 1 and 1: 3, respectively. For mmajor: mminor = 3: 1, we find that (i) the major- and minor-component solitons coexist, have comparable masses, and are roughly concentric. (ii) The soliton peak density is significantly lower than the single-component counterpart, leading to a smoother soliton-to-halo transition and rotation curve. (iii) The combined soliton mass of both components follows the same single-component core–halo mass relation. In dramatic contrast, for mmajor: mminor = 1: 3, a minor-component soliton cannot form with the presence of a stable major-component soliton; the total density profile, for both halo and soliton, is thus dominated by the major component and closely follows the single-component case. To support this finding, we propose a toy model illustrating that it is difficult to form a soliton in a hot environment associated with a deep gravitational potential. The work demonstrates that the extra flexibility added to the multi-component $\psi \rm {DM}$ model can resolve observational tensions over the single-component model while retaining its key features.

Theoretical Study of Proton Halo Structure and Elastic Electron Scattering Form Factor for 23Al and 27P Nuclei by Using Full Correlation Functions (Tensor Force and Short Range)

The study of proton-rich nuclei's form factors, root-mean-square radius (rms), and nuclear density distributions is the focus of this work for nuclei (23Al and 27P), use two body charge density distributions (2BCDD's). With the effects of the strong tensor force and short range, the nucleon distribution function of the two oscillating harmonic particles in a two-frequency shell model operates with two different parameters: bc for the inner (core) orbits and bv for the outer (halo) orbitals. This work demonstrated the existence of proton halo nuclei for the nuclei (23Al and 27P) in the shell (2s1/2), and the computed proton, neutron, and matter density distributions for these nuclei both displayed the long tail of the performance. Using the Borne approximation of the plane wave, the elastic form factor of the electron scattering from the alien nucleus was calculated, this form factor is dependent on the difference in the proton density distribution of the last proton in the nucleus. The Fortran 95 power station program was used to calculate the neutrons, protons, matter density, elastic electron scattering form factor, and rms radii. The calculated outcomes for these exotic nuclei agree well with the experimental data.

Structure of low-lying states of 9Ве nucleus

Glauber's theory of multiple scattering is applied to the calculation of differential cross sections and polarization characteristics of particle scattering on light nuclei. All calculations were carried out within the framework of a reliable spectroscopic approach to nuclear reactions. Its essence consists in the use of nuclear models that reproduce practically all the spectroscopic characteristics of the nuclei under consideration. These include three-particle models of 6Li and 9Be nuclei, a many-particle shell model for nuclei with А = 6–14, and a particle-hole model of shells for nuclei with А = 15; three-body models for the 8Li and 9Li nuclei and a two-particle αt-model for the 7Li nucleus. As our experience shows, when implementing the spectroscopic approach, when the dominant mechanism of the process is also established, one can not only obtain a description of the main characteristics of the process, but also rely on the predictive nature of the theory. In the present work, the results obtained are supplemented by calculations of the structure of the low-lying 5/2+ and 5/2– levels. This allows us to draw a general conclusion: the negative parity levels in 9Be, in which the valence neutron is in the p state, do not have a halo structure; at the same time, low-lying levels of positive parity, in which the valence neutron passes into the next (2s-1d) shell, have such. A special place is occupied by our recent direct evidence of the halo structure of low-lying excited states of the 9Be nucleus with quantum numbers 1/2+ and 3/2+. Within the framework of the ααn model of the 9-Be nucleus, it was shown that a valence neutron with a high probability is located at 11 fm from the center of gravity of two α-particles, while in the 3/2- ground state this distance is several times smaller. The conclusions about the structure of low-lying levels of 9Be, obtained on the basis of the ααn model, are supported by calculations of p9Be scattering: only taking into account the halo structure makes it possible to reproduce the experimental data on inelastic scattering to positive parity levels.

Revealing the Galaxy–Halo Connection through Machine Learning

Understanding the connections between galaxy stellar mass, star formation rate, and dark matter halo mass represents a key goal of the theory of galaxy formation. Cosmological simulations that include hydrodynamics, physical treatments of star formation, feedback from supernovae, and the radiative transfer of ionizing photons can capture the processes relevant for establishing these connections. The complexity of these physics can prove difficult to disentangle and obfuscate how mass-dependent trends in the galaxy population originate. Here, we train a machine-learning method called Explainable Boosting Machines (EBMs) to infer how the stellar mass and star formation rate of nearly 6 million galaxies simulated by the Cosmic Reionization on Computers project depend on the physical properties of halo mass, the peak circular velocity of the galaxy during its formation history v peak, cosmic environment, and redshift. The resulting EBM models reveal the relative importance of these properties in setting galaxy stellar mass and star formation rate, with v peak providing the most dominant contribution. Environmental properties provide substantial improvements for modeling the stellar mass and star formation rate in only ≲10% of the simulated galaxies. We also provide alternative formulations of EBM models that enable low-resolution simulations, which cannot track the interior structure of dark matter halos, to predict the stellar mass and star formation rate of galaxies computed by high-resolution simulations with detailed baryonic physics.

Investigation of neutral hydrogen distribution and neutral hydrogen halo mass relation based on IllustrisTNG50

For the sake of investigating the observational data of the universe mass distribution using neutral hydrogen as a mass tracer, it is necessary to investigate the simulation prediction of the distribution of the neutral hydrogen. In this paper, the TNG50 is selected, which is the latest released part of IllustrisTNG project, as simulation data to study the distribution of gas and neutral hydrogen as well as the relation between the halo mass and the corresponding neutral hydrogen mass contained in each halo. The results show a tendency that most of neutral hydrogen are distributed within the halo and sub-halo structures. The neutral hydrogen halo mass relation is clearly shown and the function can be will produced by the conventional HI halo mass parameterization function. Based on the analysis, this paper fills the blank of other related works with most recent TNG50 data. These results offer a guideline for the following study about the halo model and pave a path to deeper understanding and investigating the hydrogen distribution in the cosmos.

Uncovering dark matter density profiles in dwarf galaxies with graph neural networks

Dwarf galaxies are small, dark matter-dominated galaxies, some of which are embedded within the Milky Way. Their lack of baryonic matter (e.g., stars and gas) makes them perfect test beds for probing the properties of dark matter -- understanding the spatial dark matter distribution in these systems can be used to constrain microphysical dark matter interactions that influence the formation and evolution of structures in our Universe. We introduce a new method that leverages simulation-based inference and graph-based machine learning in order to infer the dark matter density profiles of dwarf galaxies from observable kinematics of stars gravitationally bound to these systems. Our approach aims to address some of the limitations of established methods based on dynamical Jeans modeling. We show that this novel method can place stronger constraints on dark matter profiles and, consequently, has the potential to weigh in on some of the ongoing puzzles associated with the small-scale structure of dark matter halos, such as the core-cusp discrepancy.

Influence of Nuclear Potential Diffuseness on the Neutron Halo Structure in Zr Isotopes near the Neutron Drip Line

Influence of Nuclear Potential Diffuseness on the Neutron Halo Structure in Zr Isotopes near the Neutron Drip Line

Three-body calculations of β decay applied to Li11

A novel practical few-body method is formulated to include isospin symmetry for nuclear halo structures. The method is designed to describe $\ensuremath{\beta}$ decay, where the basic concept of isospin symmetry facilitates a proper understanding. Both isobaric analog and antianalog states are treated. We derive general and explicit formulas for three-body systems using hyperspherical coordinates. The example of the $\ensuremath{\beta}$ decaying $^{11}\mathrm{Li}$ ($^{9}\mathrm{Li}+n+n$) is chosen as a challenging application for numerical calculations of practical interest. The detailed results are compared to existing experimental data, and good agreement is found at high excitation energies, where the isobaric analog and antianalog states are situated in the daughter nucleus. An interpretation of the decay pattern at lower excitation energies is suggested. Decays of the $^{9}\mathrm{Li}$ core and the two halo neutrons are individually treated and combined with the daughter system with almost unique isospin, which we predict to be broken by about $0.4%$ probability. Properties of decay products are predicted as possible future tests of this model.

Microscopic study of fusion reactions with a weakly bound nucleus: Effects of deformed halo

We present a microscopic study on the fusion reactions C14,15+Th232 by emphasizing the effect of deformed halo structure on reaction dynamics within the framework of time-dependent density functional theory. The internuclear potentials are obtained by using the density-constraint frozen Hartree-Fock approach and then are adopted to calculate the fusion cross sections of C14,15+Th232, taking all the orientations of deformed reactants into account. Our microscopic calculations not only reproduce the enhancement of fusion cross sections at sub-barrier energies without any adjustable parameters, but also reveal the underlying mechanism of this enhancement, which is driven by the deformed halo structure of C15. More interestingly, by performing particle number projection based on the wave functions from time-dependent Hartree-Fock simulation, we find that the one-neutron transfer probabilities are more sensitive to the orientations of C15 than Th232, indicating the notable effects of halo structure on the reaction dynamics.Received 30 August 2022Accepted 17 November 2022DOI:https://doi.org/10.1103/PhysRevC.107.L011601©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNuclear density functional theoryNuclear reactionsUnstable nuclei induced nuclear reactionsNuclear Physics

Cosmic Reionization on Computers: Baryonic Effects on Halo Concentrations during the Epoch of Reionization

Baryons both increase halo concentration through adiabatic contraction and expel mass through feedback processes. However, it is not well understood how the radiation fields prevalent during the epoch of reionization affect the evolution of concentration in dark matter halos. We investigate how baryonic physics during the epoch of reionization modify the structure of dark matter halos in the Cosmic Reionization On Computers (CROC) simulations. We use two different measures of halo concentration to quantify the effects. We compare concentrations of halos matched between full-physics simulations and dark-matter-only simulations with identical initial conditions between 5 ≤ z ≤ 9. Baryons in full-physics simulations do pull matter toward the center, increasing the maximum circular velocity compared to dark-matter-only simulations. However, their overall effects are much less than if all the baryons were simply centrally concentrated indicating that heating processes efficiently counteract cooling effects. Finally, we show that the baryonic effects on halo concentrations at z ≈ 5 are relatively insensitive to environmental variations of reionization history. These results are pertinent to models of galaxy–halo connection during the epoch of reionization.

Effect of casting temperature on halo in the solidification microstructure of direct-chill casting Al-16.5Si-4.5Cu-0.6Mg-0.1Zr alloys

The effect of casting temperature on the halo structure of direct-chill (DC) casting Al-16.5Si-4.5Cu-0.6Mg-0.1Zr alloys was investigated. The results indicated that the microstructure consists of fine primary Si, α-Al dendrite halo, and fine fibrous coupled eutectic structure, Al2Cu, and Al8FeMg3Si6 phase. The formation of halos was systematically analyzed. The temperature gradient at the solid–liquid interface front played an essential role in the development and growth of the halo. As the casting temperature elevated, the temperature gradient of the solid–liquid interface front increased, the solid–liquid interface became stable, the α-Al dendrite halo was less developed, the number of large-sized Si atomic clusters in the melt decreased and the growth of primary Si was inhibited.

Unravelling the interplay between SIDM and baryons in MW haloes: defining where baryons dictate heat transfer

ABSTRACT We present a new set of cosmological zoom-in simulations of a Milky Way (MW)-like galaxy that for the first time include elastic velocity-dependent self-interacting dark matter (SIDM) and IllustrisTNG physics. With these simulations, we investigate the interaction between SIDM and baryons and its effects on the galaxy evolution process. We also introduce a novel set of modified dark matter-only simulations that can reasonably replicate the effects of fully realized hydrodynamics on the DM halo while simplifying the analysis and lowering the computational cost. We find that baryons change the thermal structure of the central region of the halo to a greater extent than the SIDM scatterings for MW-like galaxies. Additionally, we find that the new thermal structure of the MW-like halo causes SIDM to create cuspier central densities rather than cores because the SIDM scatterings remove the thermal support by transferring heat away from the centre of the galaxy. We find that this effect, caused by baryon contraction, begins to affect galaxies with a stellar mass of 108 M⊙ and increases in strength to the MW-mass scale.

Spatial structure and dynamical state of the old open cluster Collinder 261 based on a clustering method

Abstract In this paper, we investigate the memberships, spatial structure, and dynamical state of the old open cluster Collinder 261 (8 Gyr) based on Gaia-DR3 data. We develop a robust clustering method to calculate membership probabilities for 24858 sample stars within 20′ of the cluster center. We can identify 2619 likely cluster members (including 54 blue stragglers) down to G ∼ 20 mag. We use a Monte Carlo simulation method to estimate a distance of 2909 ± 90 pc for the cluster based on 281 high-probability members (P > 0.9). We find that the detectable cluster radius (Rcl) is at least 14′ (∼11.8 pc), which is much larger than previously thought. Based on the obtained cluster members, the core and tidal radii of the cluster are determined to be $R_{\rm c}={3{^{\prime }_{.}}4}\pm {0.1}$ (∼2.9 ± 0.1 pc) and $R_{\rm t}={19{^{\prime }_{.}}8}\pm {1{^{\prime }_{.}}9}$ (∼16.8 ± 1.6 pc), respectively. A concentration parameter of log (Rt/Rc) ∼0.76 is determined, indicating that Collinder 261 has formed a clear core–halo structure, but its spatial structure is much looser than the old open clusters M 67 (4 Gyr) and NGC 188 (7 Gyr). We also find that the membership probabilities are suitable for analyzing the mass segregation effect in the cluster. The orbit parameters show that Collinder 261 is moving along a near-circular orbit (e ∼ 0.025) well inside the solar circle (Rp ∼ 6.928 kpc, Ra ∼ 7.285 kpc), and it can reach a maximum height of Zmax ∼ 533 pc from the Galactic plane.

Gravitational scattering of the sterile neutrino halo dark matter

ABSTRACT A recent study shows that gravitational scattering of dark matter, in the form of massive objects with mass m ∼ 103–104M⊙, could provide a possible solution to alleviate the small-scale structure problems of cold dark matter. The scattering cross-section is velocity-dependent so that this scenario can explain why self-interaction of dark matter is significant in dwarf galaxies, but not in massive galaxies and galaxy clusters. In this Letter, we show that this kind of dark massive objects could be made of sterile neutrinos with a possible rest mass range mν ∼ 7.6 keV–71 MeV. This mass range generally satisfies most of the current observational constraints. The entire structure of the sterile neutrino haloes can be simply predicted from standard physics.

Deformation and hyperon halo in hypernuclei

The effects of deformation and the change of the nuclear core on the hyperon binding and halo structure in single-$\mathrm{\ensuremath{\Lambda}}$ $p$-shell hypernuclei are studied for the C hyperisotopes and $N=6$ hyperisotones in the framework of the deformed Skyrme-Hartree-Fock approach with combinations of the $NN$ interactions SIII, SGII, SkI4 and the $\mathrm{\ensuremath{\Lambda}}N$ interactions LY1 and SLL4, respectively. Deformation causes more deeply bound states with smaller extension of the density distributions and radii. The possibility of deformed halo structures of $\mathrm{\ensuremath{\Lambda}}$ $1p$ states in hypernuclei up to a mass number $A=15$ is found.

The ground state properties of some exotic nuclei studied by the two-body model

The ground state properties including the density distributions of the neutrons, protons and matter as well as the corresponding root mean square (rms) radii of proton-rich halo candidates 8B, [Formula: see text]N, [Formula: see text]Al and [Formula: see text]P have been studied by the single particle Bear–Hodgson (BH) wave functions with the two-body model of [Formula: see text]. It is found that the rms radii of these proton-rich nuclei are reproduced well by this model and the radial wave functions describe the long tail of the proton and matter density distributions. These results indicate that this model achieves a suitable description of the possible halo structure. The plane wave Born approximation (PWBA) has been used to compute the elastic charge form factors.

Line-of-sight Elongation and Hydrostatic Mass Bias of the Frontier Fields Galaxy Cluster Abell 370

We present a detailed weak-lensing and X-ray study of the Frontier Fields galaxy cluster Abell 370, one of the most massive known lenses on the sky, using wide-field BR C z′ Subaru/Suprime-Cam and Chandra X-ray observations. By combining two-dimensional (2D) shear and azimuthally averaged magnification constraints derived from Subaru data, we perform a lensing mass reconstruction in a free-form manner, which allows us to determine both the radial structure and 2D morphology of the cluster mass distribution. In a triaxial framework assuming a Navarro–Frenk–White density profile, we constrain the intrinsic structure and geometry of the cluster halo by forward modeling the reconstructed mass map. We obtain a halo mass M 200 = (1.54 ± 0.29) ×1015 h −1 M ⊙, a halo concentration c 200 = 5.27 ± 1.28, and a minor–major axis ratio q a = 0.62 ± 0.23 with uninformative priors. Using a prior on the line-of-sight alignment of the halo major axis derived from binary merger simulations constrained by multi-probe observations, we find that the data favor a more prolate geometry with lower mass and lower concentration. From triaxial lens modeling with the line-of-sight prior, we find a spherically enclosed gas mass fraction of f gas = (8.4 ± 1.0)% at 0.7 h −1 Mpc ∼ 0.7r 500. When compared to the hydrostatic mass estimate (M HE) from Chandra observations, our triaxial weak-lensing analysis yields spherically enclosed mass ratios of 1 − b ≡ M HE/M WL = 0.56 ± 0.09 and 0.51 ± 0.09 at 0.7 h −1 Mpc with and without using the line-of-sight prior, respectively. Since the cluster is in a highly disturbed dynamical state, this represents the likely maximum level of hydrostatic bias in galaxy clusters.

Infrared Excess of a Large OB Star Sample

The infrared (IR) excess from OB stars is commonly considered to be a contribution from ionized stellar wind or circumstellar dust. With the newly published Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST)-OB catalog and Galactic O-Star Spectroscopic Survey data, this work steps further on understanding the IR excess of OB stars. Based on a forward-modeling approach comparing the spectral slope of observational spectral energy distributions and photospheric models, 1147 stars are found to have IR excess out of 7818 stars with good-quality photometric data. After removing the objects in the sightline of dark clouds, 532 (∼7%) B-type stars and 118 (∼23%) O-type stars are identified to be true OB stars with circumstellar IR excess emission. The ionized stellar wind model and the circumstellar dust model are adopted to explain the IR excess, and Bayes factors are computed to quantitatively compare the two. It is shown that the IR excess can be accounted for by the stellar wind for about 65% cases, of which 33% by free–free emission and 32% by synchrotron radiation. Other 30% sources could have and 4% should have a dust component or other mechanisms to explain the sharp increase in flux at λ > 10 μm. The parameters of the dust model indicate a large-scale circumstellar halo structure, which implies the origin of the dust from the birthplace of the OB stars. A statistical study suggests that the proportion with IR excess in OB stars increases with the stellar effective temperature and luminosity, and that there is no systematic change in the mechanism for IR emission with stellar parameters.

Temperature-linear resistivity in twisted double bilayer graphene

We report an experimental study of carrier density ($n$), displacement field, and twist angle (\ensuremath{\theta}) dependence of temperature ($T$)-linear resistivity in twisted double-bilayer graphene (TDBG). For a large twist angle ($\ensuremath{\theta}>1.{5}^{\ensuremath{\circ}}$) where correlated insulating states are absent, we observe a $T$-linear resistivity (with a slope on the order of $\ensuremath{\sim}10\phantom{\rule{0.28em}{0ex}}\mathrm{\ensuremath{\Omega}}/\mathrm{K}$) over a wide range of carrier densities, and its slope decreases with increasing $n$, which is in agreement with the acoustic phonon scattering model semiquantitatively. The slope of $T$-linear resistivity is nonmonotonically dependent on the displacement field with a single peak structure. For a device with $\ensuremath{\theta}\ensuremath{\sim}1.{23}^{\ensuremath{\circ}}$ at which correlated states emerge, the slope of $T$-linear resistivity is found to be a maximum ($\ensuremath{\sim}100\phantom{\rule{0.28em}{0ex}}\mathrm{\ensuremath{\Omega}}/\mathrm{K}$) at the boundary of the halo structure where phase transition occurs, with signatures of continuous phase transition, Planckian dissipation, and diverging effective mass. These observations are in line with quantum critical behaviors, which might be due to symmetry-breaking instability at the critical points. Our results shed new light on correlated physics in TDBG and other twisted moir\'e systems.

Baryonic solutions and challenges for cosmological models of dwarf galaxies

Galaxies and their dark-matter haloes have posed several challenges to the dark energy plus cold dark matter (ΛCDM) cosmological model. These discrepancies between observations and theory intensify for the lowest-mass (‘dwarf’) galaxies. ΛCDM predictions for the number, spatial distribution and internal structure of low-mass dark-matter haloes have historically been at odds with observed dwarf galaxies, but this is partially expected, because many predictions modelled only the dark-matter component. Any robust ΛCDM prediction must include, hand in hand, a model for galaxy formation to understand how baryonic matter populates and affects dark-matter haloes. In this Review, we consider the most notable challenges to ΛCDM regarding dwarf galaxies, and we discuss how recent cosmological numerical simulations have pinpointed baryonic solutions to these challenges. We identify remaining tensions, including the diversity of the inner dark-matter content, planes of satellites, stellar morphologies and star-formation quenching. Their resolution, or validation as actual problems with ΛCDM, will probably require both refining of galaxy-formation models and improving numerical accuracy in simulations. Galaxies and their dark-matter haloes have posed several challenges to the dark energy plus cold dark matter (ΛCDM) cosmological model. This Review discusses the most notable challenges to ΛCDM regarding dwarf galaxies and the insights provided by recent cosmological numerical simulations.