Halo Density Research Articles

The Power of High-precision Broadband Photometry: Tracing the Milky Way Density Profile with Blue Horizontal Branch Stars in the Dark Energy Survey

Blue horizontal branch stars (BHBs), excellent distant tracers for probing the Milky Way’s halo density profile, are distinguished in the g−r0 versus (i − z)0 color space from another class of stars, blue straggler stars. We develop a Bayesian mixture model to classify BHBs using high-precision photometry data from the Dark Energy Survey Data Release 2 (DES DR2). We select ∼2100 highly probable BHBs based on their griz photometry and the associated uncertainties, and we use these stars to map the stellar halo over the Galactocentric radial range 20 kpc ≲ R ≲ 70 kpc. After excluding known stellar overdensities, we find that the number density n ⋆ of BHBs can be represented by a power-law density profile n ⋆ ∝ R −α with an index of α=4.34−0.12+0.13±0.52 , consistent with existing literature values. In addition, we examine the impact of systematic errors and the spatial inhomogeneity on the fitted density profile. Our work demonstrates the effectiveness of high-precision griz photometry in selecting BHBs. The upcoming photometric survey from the Rubin Observatory, expected to reach depths 2–3 mag greater than DES during its 10 yr mission, will enable us to investigate the density profile of the Milky Way’s halo out to the virial radius, unraveling the complex processes of formation and evolution in our Galaxy.

Exploring the impact of modified gravity on the density field and halo properties within the cosmic web

Exploring the impact of modified gravity on the density field and halo properties within the cosmic web

Dark matter induced baryonic feedback in galaxies

We demonstrate that nongravitational interactions between dark matter and baryonic matter can affect structural properties of galaxies. Detailed galaxy simulations and analytic estimates demonstrate that dark matter which collects inside white dwarf stars and ignites type Ia supernovae can substantially alter star formation, stellar feedback, and the halo density profile through a dark matter induced baryonic feedback process, distinct from usual supernova feedback in galaxies. Published by the American Physical Society 2024

Mapping the anisotropic Galactic stellar halo with blue horizontal branch stars

We used Legacy Survey photometric data to probe the stellar halo in multiple directions of the sky using a probabilistic methodology to identify blue horizontal branch (BHB) stars. The measured average radial density profile follows a double power law in the range 5 < rgc/kpc < 120, with a density break at rgc ≈ 20 kpc. This description, however, falls short, depending on the chosen line of sight, with some regions showing no signature of a break in the profile and a wide range of density slopes, such as an outer slope −5.5 ≲ αout ≲ −4, pointing towards a highly anisotropic stellar halo. This explains, in part, the wide range of density profiles reported in the literature owing to different tracers and sky coverage. Using our detailed 3D stellar halo density map, we quantified the shape of the Pisces overdensity associated with the transient wake response of the Galaxy’s (dark) halo to the Large Magellanic Cloud (LMC). Measured in the LMC’s coordinate system, Pisces stands above the background, is 60° long and 25° wide, and is aligned with the LMC’s orbit. This would correspond to a wake width of ∼32 kpc at ∼70 kpc. We do not find a statistically significant signature of the collective response in density as previously reported in the literature measured with K giant stars, despite our larger numbers. We release the catalogue constructed in this study with 95 446 possible BHB stars and their BHB probability.

Mass scaling relations for dark halos from an analytic universal outer density profile

Context. The average matter density within the turnaround scale, which demarcates where galaxies shift from clustering around a structure to joining the expansion of the Universe, is an important cosmological probe. However, a measurement of the mass enclosed by the turnaround radius is difficult. Analyses of the turnaround scale in simulated galaxy clusters place the turnaround radius at about three times the virial radius in a ΛCDM universe and at a (present-day) density contrast with the background matter density of the Universe of δ ~ 11. Assessing the mass at such extended distances from a cluster’s center is a challenge for current mass measurement techniques. Consequently, there is a need to develop and validate new mass-scaling relations, to connect observable masses at cluster interiors with masses at greater distances. Aims. Our research aims to establish an analytical framework for the most probable mass profile of galaxy clusters, leading to novel mass scaling relations, allowing us to estimate masses at larger scales. We derive such analytical mass profiles and compare them with those from cosmological simulations. Methods. We used excursion set theory, which provides a statistical framework for the density and local environment of dark matter halos, and complement it with the spherical collapse model to follow the non-linear growth of these halos. Results. The profile we developed analytically showed good agreement (better than 30%, and dependent on halo mass) with the mass profiles of simulated galaxy clusters. Mass scaling relations were obtained from the analytical profile with offset better than 15% from the simulated ones. This level of precision highlights the potential of our model for probing structure formation dynamics at the outskirts of galaxy clusters.

Halo densities and pericenter distances of the bright Milky Way satellites as a test of dark matter physics

ABSTRACT We provide new constraints on the dark matter halo density profile of Milky Way (MW) dwarf spheroidal galaxies (dSphs) using the phase-space distribution function (DF) method. After assessing the systematics of the approach against mock data from the Gaia Challenge project, we apply the DF analysis to the entire kinematic sample of well-measured MW dwarf satellites for the first time. Contrary to previous findings for some of these objects, we find that the DF analysis yields results consistent with the standard Jeans analysis. In particular, in this study we rediscover (i) a large diversity in the inner halo densities of dSphs (bracketed by Draco and Fornax), and (ii) an anticorrelation between inner halo density and pericenter distance of the bright MW satellites. Regardless of the strength of the anticorrelation, we find that the distribution of these satellites in density versus pericenter space is inconsistent with the results of the high-resolution N-body simulations that include a disc potential. Our analysis motivates further studies on the role of internal feedback and dark matter microphysics in these dSphs.

Possible existence of Rastall–Rainbow wormholes in dark matter galactic halos

The Rastall–Rainbow gravity theory has recently been proposed as a combination of the Rastall and rainbow theories. This theory can be thought as a generalization of the Rastall gravity to an energy dependent Rastall theory, and leads to an additional degrees of freedom. In this paper, we construct models that admit the wormhole geometries within this theory. We analyze the properties of static wormholes based on the profiles of dark matter halos, which was demonstrated earlier in Rahaman et al. (Eur Phys J C 74:2750, 2014) that galactic halo possesses the necessary properties in favour of the existence of wormholes. The main properties are being analyzed by considering three different kinds of halo density profiles. Our results indicate that such wormholes could potentially exist but the NEC is violated in the vicinity of the wormhole throat. We have further examined the stability of the configuration through the adiabatic sound velocity.

Charting the Galactic Acceleration Field. II. A Global Mass Model of the Milky Way from the STREAMFINDER Atlas of Stellar Streams Detected in Gaia DR3

We present an atlas and follow-up spectroscopic observations of 87 thin stream-like structures detected with the STREAMFINDER algorithm in Gaia DR3, of which 28 are new discoveries. Here, we focus on using these streams to refine mass models of the Galaxy. Fits with a double-power-law halo with the outer power-law slope set to −β h = −3 yield an inner power-law slope of −γh=-(0.97−0.21+0.17) , a scale radius of r0,h=14.7−1.0+4.7kpc , a halo density flattening q m,h = 0.75 ± 0.03, and a local dark matter density of ρ h,⊙ = 0.0114 ± 0.0007 M ⊙ pc−3. Freeing β yields β=2.53−0.16+0.42 , but this value is heavily influenced by our chosen virial mass limit. The stellar disks are found to have a combined mass of 4.20−0.53+0.44×1010M⊙ , with the thick disk contributing 12.4% ± 0.7% to the local stellar surface density. The scale lengths of the thin and thick disks are 2.17−0.08+0.18 and 1.62−0.13+0.72kpc , respectively, while their scale heights are 0.347−0.010+0.007 and 0.86−0.02+0.03kpc , respectively. The virial mass of the favored model is M200=1.09−0.14+0.19×1012M⊙ , while the mass inside of 50 kpc is M R<50 = 0.46 ± 0.03 × 1012 M ⊙. We introduce the Large Magellanic Cloud (LMC) into the derived potential models, and fit the Orphan stream therein, finding a mass for the LMC that is consistent with recent estimates. Some salient highlights include the nearby trailing arm of ω Cen, and a nearby very metal-poor stream that was once a satellite of the Sagittarius dwarf galaxy. Finally, we unambiguously detect a hot component around the GD-1 stream, consistent with it having been tidally preprocessed within its own dark matter subhalo.

Primordial Black Hole–Neutron Star Merger Rate in Modified Gravity

In this work, we investigate the merger rate of primordial black hole–neutron star (PBH-NS) binaries in two widely studied modified gravity (MG) models: Hu–Sawicki f(R) gravity and the normal branch of Dvali–Gabadadze–Porrati gravity. In our analysis, we take into account the effects of MG on the halo properties, including halo mass function, halo concentration parameter, halo density profile, and velocity dispersion of dark matter particles. We find that these MG models, due to their stronger gravitational field induced by an effective fifth force, predict enhanced merger rates compared to general relativity. This enhancement is found to be redshift-dependent and sensitive to model parameters and PBH mass and fraction. Assuming a PBH mass range of 5–50 M ⊙, we compare the predicted merger rate of PBH-NS binaries with those inferred from LIGO–Virgo–KAGRA observations of gravitational waves (GWs). We find that the merger rates obtained from MG models will be consistent with the GW observations if the abundance of PBHs is relatively large, with the exact amount depending on the MG model and its parameter values, as well as PBH mass. We also establish upper limits on the abundance of PBHs in these MG frameworks while comparing them with the existing non-GW constraints, which can potentially impose even more stringent constraints.

Taking the pulse of the outer Milky Way with the Halo Outskirts With Variable Stars (HOWVAST) survey: an RR Lyrae density profile out to &amp;gt;200 kpc

ABSTRACT In order to constrain the evolutionary history of the Milky Way, we hunt for faint RR Lyrae stars (RRLs) using Dark Energy Camera data from the High cadence Transient Survey and the Halo Outskirts With Variable Stars survey. We report the detection of $\sim$500 RRLs, including previously identified stars and $\sim$90 RRLs not yet reported. We identify nine new RRLs beyond 100 kpc from the Sun, most of which are classified as fundamental-mode pulsators. The periods and amplitudes of the distant RRLs do not place them in either one of the two classical Oosterhoff groups, but in the Oosterhoff intermediate region. We detect two groups of clumped distant RRLs with similar distances and equatorial coordinates, which we interpret as an indication of their association with undiscovered bound or unbound satellites. We study the halo density profile using spheroidal and ellipsoidal ($q=0.7$) models, following a Markov chain Monte Carlo methodology. For a spheroidal halo, our derived radial profile is consistent with a broken power law with a break at $18.1^{+2.1}_{-1.1}$ kpc separating the inner and the outer halo, and an outer slope of $-4.47^{+0.11}_{-0.18}$. For an ellipsoidal halo, the break is located at $24.3^{+2.6}_{-3.2}$ kpc and the outer slope is $-4.57^{+0.17}_{-0.25}$. The break in the density profile is a feature visible in different directions of the halo. The similarity of these radial distributions with previous values reported in the literature seems to depend on the regions of the sky surveyed (direction and total area) and halo tracer used. Our findings are compatible with simulations and observations that predict that the outer regions of Milky Way-like galaxies are mainly composed of accreted material.

Wormhole solutions under the effect of dark matter in f(R, L m ) gravity

In the background of f(R, L m ) gravity, this work investigates three distinct dark matter halo profiles to test the possibility of generalised wormhole geometry within the galactic halo regions. The current study aims to accomplish these goals by examining various dark matter profiles including universal rotation curves (URC), Navarro–Frenk–White (NFW) model-I, and NFW model-II inside two distinct f(R, L m ) gravity models. According to the f(R,Lm)=R2+Lmα model, the dark matter (DM) halo density profiles produce suitable shape functions that meet all the necessary requirements for exhibiting the wormhole geometries with appropriate choice of free parameters. In addition, to examine DM profiles under the f(R,Lm)=R2+(1+λR)Lm model, we consider a specific shape function. Further, we observed that the derived solution from both two models violates the null energy constraints, confirming that the DM supports wormholes to maintain in the galactic halo.

Stellar halo density with LAMOST K and M giants

Aims. We derive the morphology of the stellar component in the outer halo volume, and search for possible overdensities due to substructures therein. Methods. We made use of some of the data releases of the spectroscopic survey LAMOST DR8-DR9 in tandem with distance determinations for two subsamples, that is, of K-giants and M-giants, respectively, making up 60 000 stars. These distance are obtained through Bayesian techniques that derive absolute magnitudes as a function of measured spectroscopic parameters. Our calculation of the density from these catalogues requires: (1) derivation of the selection function; and (2) a correction for the convolution of the distance errors, which we carried out with Lucy’s inversion of the corresponding integral equation. Results. The stellar density distribution of the outer halo (distance to the Galactic centre, rG, of between 25 and 90 kpc) is a smooth monotonously decreasing function with a dependence of approximately ρ ∝ rG−n, with n = 4.6 ± 0.4 for K-giants and n = 4.5 ± 0.2 for M-giants, and with a insignificant oblateness. The value of n is independent of the angular distance to the Sagittarius tidal stream plane, which is what would be expected if such a stream did not exist in the anticenter positions or had a negligible imprint in the density distribution in the outer halo. Apart from random fluctuations or minor anomalies in some lines of sight, we do not see substructures superimposed in the outer halo volume within the resolution that we are using and limited by the error bars. This constrains the mass of over- and under-densities in the outer halo to be of ≲103 M⊙ deg−2, whereas the total mass of the stellar halo, including inner and outer parts, is ∼7 × 108 M⊙.

Impact of dark matter galactic halo models on wormhole geometry within f(Q,T) gravity

This study investigates the possible existence of wormhole solutions with dark matter galactic halo profiles in the background of f(Q,T) gravity. The primary focus of the current study is to find the significance of dark matter (DM) in the search for traversable wormhole solutions within galactic halos. Various dark matter profiles, such as Universal Rotation Curves (URC), Navarro-Frenk-White (NFW) model-I, and NFW model-II, are examined within two different f(Q,T) models. The DM halo density profiles generate appropriate shape functions under the linear model that satisfy all the essential conditions for presenting the wormhole geometries. Apart from that, we take into account an embedded wormhole-specific shape function to inspect DM profiles under the non-linear model. We noticed that the null energy conditions are violated by the obtained solution from each model, which confirms that the DM support wormholes to sustain in the galactic halo. The findings reveal that the solutions obtained for different density profiles of dark matter halos within generalized symmetric teleparallel gravity demonstrate viability.

Stochastic gravitational wave background from the collisions of dark matter halos

We investigate the effect of the dark matter (DM) halos collisions, namely collisions of galaxies and galaxy clusters, through gravitational bremsstrahlung, on the stochastic gravitational wave background. We first calculate the gravitational wave signal of a single collision event, assuming point masses and linear perturbation theory. Then we proceed to the calculation of the energy spectrum of the collective effect of all dark matter collisions in the Universe. Concerning the DM halo collision rate, we show that it is given by the product of the number density of DM halos, which is calculated by the extended Press–Schechter (EPS) theory, with the collision rate of a single DM halo, which is given by simulation results, with a function of the linear growth rate of matter density through cosmological evolution. Hence, integrating over all mass and distance ranges, we finally extract the spectrum of the stochastic gravitational wave background created by DM halos collisions. As we show, the resulting contribution to the stochastic gravitational wave background is of the order of hc≈10-29\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$h_{c} \\approx 10^{-29}$$\\end{document} in the band of f≈10-15Hz\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f \\approx 10^{-15} Hz$$\\end{document}. However, in very low frequency band, it is larger. With current observational sensitivity it cannot be detected.

Explaining Dark Matter Halo Density Profiles with Neural Networks.

We use explainable neural networks to connect the evolutionary history of dark matter halos with their density profiles. The network captures independent factors of variation in the density profiles within a low-dimensional representation, which we physically interpret using mutual information. Without any prior knowledge of the halos' evolution, the network recovers the known relation between the early time assembly and the inner profile and discovers that the profile beyond the virial radius is described by a single parameter capturing the most recent mass accretion rate. The results illustrate the potential for machine-assisted scientific discovery in complicated astrophysical datasets.

Free-floating ‘planets’ in the macrolensed quasar Q2237+0305

ABSTRACT It has been claimed that the variability of field quasars resembles gravitational lensing by a large cosmological population of free-floating planets with mass $\sim\!\! 10\ {\rm M}_{\oplus }$. However, Galactic photometric monitoring experiments, on the other hand, exclude a large population of such planetary-mass gravitational lenses. These apparently contradictory pieces of evidence can be reconciled if the objects under consideration have a mean column density that lies between the critical column densities for gravitational lensing in these two contexts. Dark matter in that form is known to be weakly collisional, so a core develops in galaxy halo density profiles, and a preferred model has already been established. Here, we consider what such a model implies for Q2237+0305, which is the best-studied example of a quasar that is strongly lensed by an intervening galaxy. We construct microlensing magnification maps appropriate to the four macro-images of the quasar – all of which are seen through the bulge of the galaxy. Each of these maps exhibits a caustic network arising from the stars, plus many small, isolated caustics arising from the free-floating ‘planets’ in the lens galaxy. The ‘planets’ have little influence on the magnification histograms but a large effect on the statistics of the magnification gradients. We compare our predictions to the published Optical Gravitational Lensing Experiment (OGLE) photometry of Q2237+0305 and find that these data are consistent with the presence of the hypothetical ‘planets’. However, the evidence is relatively weak because the OGLE data set is not well suited to testing our predictions and requires low-pass filtering for this application. New data from a large, space-based telescope are desirable to address this issue.

From particles to orbits: precise dark matter density profiles using dynamical information

ABSTRACT We introduce a new method to calculate dark matter halo density profiles from simulations. Each particle is ‘smeared’ over its orbit to obtain a dynamical profile that is averaged over a dynamical time, in contrast to the traditional approach of binning particles based on their instantaneous positions. The dynamical and binned profiles are in good agreement, with the dynamical approach showing a significant reduction in Poisson noise in the innermost regions. We find that the inner cusps of the new dynamical profiles continue inward all the way to the softening radius, reproducing the central density profile of higher resolution simulations within the 95 per cent confidence intervals, for haloes in virial equilibrium. Folding in dynamical information thus provides a new approach to improve the precision of dark matter density profiles at small radii, for minimal computational cost. Our technique makes two key assumptions that the halo is in equilibrium (phase mixed) and the potential is spherically symmetric. We discuss why the method is successful despite strong violations of spherical symmetry in the centres of haloes, and explore how substructures disturb equilibrium at large radii.

Dark matter halo mass functions and density profiles from mass and energy cascade

Halo abundance and structure play a central role for modeling structure formation and evolution. Without relying on a spherical or ellipsoidal collapse model, we analytically derive the halo mass function and cuspy halo density (inner slope of −4/3) based on the mass and energy cascade theory in dark matter flow. The hierarchical halo structure formation leads to halo or particle random walk with a position-dependent waiting time tau _g. First, the inverse mass cascade from small to large scales leads to the halo random walk in mass space with tau _gpropto m_h^{-lambda }, where m_h is the halo mass and lambda is a halo geometry parameter with predicted value of 2/3. The corresponding Fokker-Planck solution for halo random walk in mass space gives rise to the halo mass function with a power-law behavior on small scale and exponential decay on large scale. This can be further improved by considering two different lambda for haloes below and above a critical mass scale m_h^*, i.e. a double-lambda halo mass function. Second, a double-gamma density profile can be derived based on the particle random walk in 3D space with a position-dependent waiting time tau _g propto Phi (r)^{-1} propto r^{-gamma }, where Phi is the gravitational potential and r is the particle distance to halo center. Theory predicts gamma =2/3 that leads to a cuspy density profile with an inner slope of −4/3, consistent with the predicted scaling laws from energy cascade. The Press-Schechter mass function and Einasto density profile are just special cases of proposed models. The small scale permanence can be identified due to the scale-independent rate of mass and energy cascade, where density profiles of different halo masses and redshifts converge to the -4/3 scaling law (rho _h propto r^{-4/3}) on small scales. Theory predicts the halo number density scales with halo mass as propto m_h^{-1.9}, while the halo mass density scales as propto m_h^{4/9}. Results were compared against the Illustris simulations. This new perspective provides a theory for nearly universal halo mass functions and density profiles.

Fast forward modeling of neutral beam injection and halo formation including full Balmer-α emission prediction at W7-X

A full collisional-radiative (CR) neutral beam injection model based on Gaussian pencil (Gausscil) beams and a diffusive CR neutral halo model are presented. The halo is a neutral cloud around the neutral beam forming due to multiple charge exchange (CX) reactions. Both models do not rely on Monte-Carlo techniques and are thereby orders of magnitude faster than commonly used models. To model the neutral halo a system of coupled diffusion equations is solved numerically, enforcing mixed boundary conditions. From the equilibrium hydrogen neutral densities in the second excited energy state (n = 3), the Balmer-α emission intensity is calculated and the full spectrum is predicted, including effects as Doppler shifts and broadening due to the complex neutral beam geometry and the motional Stark effect (MSE) from the magnetic field. All forward models are implemented in the Minerva [1] Bayesian analysis framework to enable detailed multivariant inference from Balmer-α spectroscopy data. The modeled neutral beam and halo densities are successfully verified against calculations with a validated Monte-Carlo code for the W7-X beam and plasma geometry, especially proving the validity of the halo diffusion ansatz. A comparison of the predicted emission spectra with the experimental data proves the accuracy of the implemented model. All important parameters defining the neutral beams are inferred and compared to available reference values.

Is a Recently Discovered H i Cloud near M94 a Starless Dark Matter Halo?

Observations with the Five-hundred-meter Aperture Spherical Telescope have revealed the presence of a marginally resolved source of 21 cm emission from a location from the M94 galaxy, without a stellar counterpart down to the surface brightness limit of the DESI Imaging Legacy Survey (∼29.15 mag arcsec−2 in the g band). The system (hereafter Cloud-9) has round column density isocontours and a line width consistent with thermal broadening from gas at T ∼ 2 × 104 K. These properties are unlike those of previously detected dark H i clouds and similar to the expected properties of REionization-Limited-H i Clouds (RELHICs), namely, starless dark matter (DM) halos filled with gas in hydrostatic equilibrium and in thermal equilibrium with the cosmic ultraviolet background. At the distance of M94, d ∼ 4.7 Mpc, we find that Cloud-9 is consistent with being a RELHIC inhabiting a Navarro–Frenk–White (NFW) DM halo of mass M 200 ∼ 5 × 109 M ⊙ and concentration c NFW ∼ 13. Although the agreement between the model and observations is good, Cloud-9 appears to be slightly, but systematically, more extended than expected for ΛCDM RELHICs. This may imply either that Cloud-9 is much closer than implied by its recessional velocity, v CL9 ∼ 300 km s−1, or that its halo density profile is flatter than NFW, with a DM mass deficit greater than a factor of 10 at radii r ≲ 1 kpc. Further observations may aid in constraining these scenarios better and help elucidate whether Cloud-9 is the first ever observed RELHIC, a cornerstone prediction of the ΛCDM model on the smallest scales.