Central Dark Matter Density Profile Research Articles

Bursting with Feedback: The Relationship between Feedback Model and Bursty Star Formation Histories in Dwarf Galaxies

Due to their inability to self-regulate, ultrafaint dwarfs are sensitive to prescriptions in subgrid physics models that converge and regulate at higher masses. We use high-resolution cosmological simulations to compare the effect of bursty star formation histories (SFHs) on dwarf galaxy structure for two different subgrid supernova (SN) feedback models, superbubble and blastwave, in dwarf galaxies with stellar masses from 5000 < M */M ⊙ < 109. We find that in the “MARVEL-ous Dwarfs” suite both feedback models produce cored galaxies and reproduce observed scaling relations for luminosity, mass, and size. Our sample accurately predicts the average stellar metallicity at higher masses, however low-mass dwarfs are metal poor relative to observed galaxies in the Local Group. We show that continuous bursty star formation and the resulting stellar feedback are able to create dark matter (DM) cores in the higher dwarf galaxy mass regime, while the majority of ultrafaint and classical dwarfs retain cuspy central DM density profiles. We find that the effective core formation peaks at M */M halo ≃ 5 × 10−3 for both feedback models. Both subgrid SN models yield bursty SFHs at higher masses; however, galaxies simulated with superbubble feedback reach maximum mean burstiness values at lower stellar mass fractions relative to blastwave feedback. As a result, core formation may be better predicted by stellar mass fraction than the burstiness of SFHs.

New Constraints on the Dark Matter Density Profiles of Dwarf Galaxies from Proper Motions of Globular Cluster Streams

The central density profiles in dwarf galaxy halos depend strongly on the nature of dark matter (DM). Recently, in Malhan et al. we employed N-body simulations to show that the cuspy cold DM subhalos predicted by cosmological simulations can be differentiated from cored subhalos using the properties of accreted globular cluster (GC) streams since these GCs experience tidal stripping within their parent halos prior to accretion onto the Milky Way. We previously found that clusters that are accreted within cuspy subhalos produce streams with larger physical widths and higher dispersions in line-of-sight velocity and angular momentum than streams that are accreted within cored subhalos. Here, we use the same suite of simulations to demonstrate that the dispersion in the tangential velocities of streams () is also sensitive to the central DM density profiles of their parent dwarfs and GCs that they were accreted from; cuspy subhalos produce streams with larger than those accreted inside cored subhalos. Using Gaia EDR3 observations of multiple GC streams we compare their values with simulations. The measured values are consistent with both an “in situ” origin and with accretion inside cored subhalos of M ∼ 108–9 M ⊙ (or very low-mass cuspy subhalos of mass ∼108 M ⊙). Despite the large current uncertainties in , we find a low probability that any of the progenitor GCs were accreted from cuspy subhalos of M ≳ 10 9 M ⊙. The uncertainties on Gaia tangential velocity measurements are expected to decrease in future and will allow for stronger constraints on subhalo DM density profiles.

Probing the nature of dark matter with accreted globular cluster streams

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.

Dark matter around primordial black hole at the radiation-dominated stage

The accumulation of dark matter particles near the primordial black holes starts at the radiation-dominated cosmological stage and produces the central density spikes. The spikes can be the bright gamma-ray sources due to dark matter annihilation. We present the self-consistent derivation of the equation of motion of particle in the metrics of primordial black hole immersed into cosmological background. By numerical solution of this equation we find the central dark matter density profile. The density growth is suppressed in the central part of the profile compared with previous calculations.

Mass models of gas-rich void dwarf galaxies

ABSTRACT We construct mass models of eight gas rich dwarf galaxies that lie in the Lynx–Cancer void. From NFW fits to the dark matter halo profile, we find that the concentration parameters of haloes of void dwarf galaxies are similar to those of dwarf galaxies in normal density regions. We also measure the slope of the central dark matter density profiles, obtained by converting the rotation curves derived using 3D (fat) and 2D (ROTCUR) tilted ring fitting routines, into mass densities. We find that the average slope (α = −1.39 ± 0.19), obtained from 3D fitting is consistent with that expected from an NFW profile. On the other hand, the average slope measured using the 2D approach is closer to what would be expected for an isothermal profile. This suggests that systematic effects in velocity field analysis have a significant effect on the slope of the central dark matter density profiles. Given the modest number of galaxies we use for our analysis, it is important to check these results using a larger sample.

Correlations in the matter distribution in CLASH galaxy clusters

Abstract We study the total and dark matter (DM) density profiles as well as their correlations for a sample of 15 high-mass galaxy clusters by extending our previous work on several clusters from Newman et al. Our analysis focuses on 15 CLASH X-ray-selected clusters that have high-quality weak- and strong-lensing measurements from combined Subaru and Hubble Space Telescope observations. The total density profiles derived from lensing are interpreted based on the two-phase scenario of cluster formation. In this context, the brightest cluster galaxy (BCG) forms in the first dissipative phase, followed by a dissipationless phase where baryonic physics flattens the inner DM distribution. This results in the formation of clusters with modified DM distribution and several correlations between characteristic quantities of the clusters. We find that the central DM density profiles of the clusters are strongly influenced by baryonic physics as found in our earlier work. The inner slope of the DM density for the CLASH clusters is found to be flatter than the Navarro–Frenk–White profile, ranging from α = 0 . 30 to 0.79. We examine correlations of the DM density slope α with the effective radius R e and stellar mass M e of the BCG, finding that these quantities are anti-correlated with a Spearman correlation coefficient of ∼ − 0 . 6 . We also study the correlation between R e and the cluster halo mass M 500 , and the correlation between the total masses inside 5 kpc and 100 kpc. We find that these quantities are correlated with Spearman coefficients of 0.68 and 0.64, respectively. These observed correlations are in support of the physical picture proposed by Newman et al.

A model for the mass and distribution of particles in dark matter halos

This model is intended for dark-matter-dominated galaxies and galaxy clusters for which the centrifugal force caused by system rotation is negligible. Such systems, ostensibly dark matter halos, would tend to be spherical. Consider a uniform sphere of identical, massive particles in equilibrium (not contracting or expanding). In the quantum model, gravitation pulls the particles together and quantum uncertainty pushes them apart. In the corresponding classical model, gravitation pulls the particles together and thermal motion pushes them apart. This model provides an expression for particle mass as a function of the total mass and density of the system and its quantum state or temperature. Using the measured total mass and density of our dark-matter-dominated galaxy, and assuming the system is in the ground state, the particle mass is found to be 10.5 eV and the temperature 0.042 K. This represents the lowest possible system temperature and particle mass. If, on the other hand, the system is in equilibrium with the cosmic microwave background, the particle mass is found to be 693 eV. This range of inferred particle masses supports the hypothesis of “low-mass dark matter” with approximate mass 100 eV. However, the system temperature is not presently known so it is possible that the temperature is higher and, consequently, the particles are heavier. The average speed of the particles is found to be approximately 1/1000 the speed of light in our galaxy. Remarkably, this result does not depend on the system temperature and, therefore, does not depend on the particle mass. The extension of this model to variable density provides a straightforward solution to the “core-cusp problem” because the distribution of dark matter that minimizes the system energy has a flat central dark matter density profile.

The case for a cold dark matter cusp in Draco

We use a new mass modelling method, GravSphere, to measure the central dark matter density profile of the Draco dwarf spheroidal galaxy. Draco's star formation shut down long ago, making it a prime candidate for hosting a 'pristine' dark matter cusp, unaffected by stellar feedback during galaxy formation. We first test GravSphere on a suite of tidally stripped mock 'Draco'-like dwarfs. We show that we are able to correctly infer the dark matter density profile of both cusped and cored mocks within our 95% confidence intervals. While we obtain only a weak inference on the logarithmic slope of these density profiles, we are able to obtain a robust inference of the amplitude of the inner dark matter density at 150pc, $\rho_{\rm DM}(150\,{\rm pc})$. We show that, combined with constraints on the density profile at larger radii, this is sufficient to distinguish a $\Lambda$ Cold Dark Matter ($\Lambda$CDM) cusp $-$ that has $\rho_{\rm DM}(150\,{\rm pc}) > 1.8 \times 10^8\,{\rm M}_\odot \,{\rm kpc}^{-3}$ $-$ from alternative dark matter models that have lower inner densities. We then apply GravSphere to the real Draco data. We find that Draco has an inner dark matter density of $\rho_{\rm DM}(150\,{\rm pc}) = 2.4_{-0.6}^{+0.5} \times 10^8\,{\rm M}_\odot \,{\rm kpc}^{-3}$, consistent with a $\Lambda$CDM cusp. Using a velocity independent SIDM model, calibrated on $\Lambda$SIDM cosmological simulations, we show that Draco's high central density gives an upper bound on the SIDM cross section of $\sigma/m < 0.57\,{\rm cm}^2\,{\rm g}^{-1}$ at 99% confidence. We conclude that the inner density of nearby dwarf galaxies like Draco provides a new and competitive probe of dark matter models.

Dynamical evolution of primordial dark matter haloes through mergers

Primordial dark matter (DM) haloes are the smallest gravitationally bound DM structures from which the first stars, black holes, and galaxies form and grow in the early universe. However, their structures are sensitive to the free streaming scale of DM, which in turn depends on the nature of DM particles. In this work, we test the hypothesis that the slope of the central cusps in primordial DM haloes near the free streaming scale depends on the nature of merging process. By combining and analysing data from a cosmological simulation with the cutoff in the small-scale matter power spectrum as well as a suite of controlled, high-resolution simulations of binary mergers, we find that (1) the primordial DM haloes form preferentially through major mergers in radial orbits; (2) their central DM density profile is more susceptible to a merging process compared to that of galaxy and cluster-size DM haloes; (3) consecutive major mergers drive the central density slope to approach the {\it universal} form characterized by the NFW profile, which is shown to be robust to the impacts of mergers and serves an attractor solution for the density structure of DM haloes. Our work highlights the importance of dynamical processes on the structure formation during the Dark Ages.

Cores and revived cusps of dark matter haloes in disc galaxy formation through clump clusters

Cusp-core problem is a controversial problem on galactic dark matter haloes. Cosmological N-body simulations has demonstrated that galactic dark matter haloes have a cuspy density profile at the centre. However, baryonic physics may affect the dark matter density profile. For example, it was suggested that adiabatic contraction of baryonic gas makes the dark matter cusp steeper. However, it is still an open question if the gas falls into the galactic centre in smooth adiabatic manner. Recent numerical studies suggested that disc galaxies might experience clumpy phase in their early stage of the disc formation, which could also explain clump clusters and chain galaxies observed in high redshift Universe. In this letter, using numerical simulations with an isolated model, we study how the dark matter halo responds to these clumpy nature of baryon component in disc galaxy formation through the clump cluster phase. Our simulation demonstrates that such clumpy phase leads to a shallower density profile of the dark matter halo in the central region while clumps fall into the centre due to dynamical friction. This mechanism helps to make the central dark matter density profile shallower in the galaxies whose virial mass is as large as 5.0*10^11 solar masses. This phenomenon is caused by reaction to dynamical friction of the stellar clumps against the dark matter halo. The halo draws the clumps into the galactic centre, while kinematically heated by the clumps. We additionally run a dark matter only simulation excluding baryonic component and confirm that the resultant shallower density profile is not due to numerical artifact in the simulation, such as two-body relaxation.

DISSIPATIONAL VERSUS DISSIPATIONLESS GALAXY FORMATION AND THE DARK MATTER CONTENT OF GALAXIES

We examine two extreme models for the build-up of the stellar component of luminous elliptical galaxies. In one case, we assume the build-up of stars is dissipational, with centrally accreted gas radiating away its orbital and thermal energy; the dark matter halo will undergo adiabatic contraction and the central dark matter density profile will steepen. For the second model, we assume the central galaxy is assembled by a series of dissipationless mergers of stellar clumps that have formed far from the nascent galaxy. In order to be accreted, these clumps lose their orbital energy to the dark matter halo via dynamical friction, thereby heating the central dark matter and smoothing the dark matter density cusp. The central dark matter density profiles differ drastically between these models. For the isolated elliptical galaxy, NGC 4494, the central dark matter densities follow the power-laws r^(-0.2) and r^(-1.7) for the dissipational and dissipationless models, respectively. By matching the dissipational and dissipationless models to observations of the stellar component of elliptical galaxies, we examine the relative contributions of dissipational and dissipationless mergers to the formation of elliptical galaxies and look for observational tests that will distinguish between these models. Comparisons to strong lensing brightest cluster galaxies yield median M*/L_B ratios of 2.1+/-0.8 and 5.2+/-1.7 at z=0.39 for the dissipational and dissipationless models, respectively. For NGC 4494, the best-fit dissipational and dissipationless models have M*/L_B=2.97 and 3.96. Comparisons to expected stellar mass-to-light ratios from passive evolution and population syntheses appear to rule out a purely dissipational formation mechanism for the central stellar regions of giant elliptical galaxies.

Is There Evidence for Flat Cores in the Halos of Dwarf Galaxies? The Case of NGC 3109 and NGC 6822

Two well-studied dwarf galaxies, NGC 3109 and NGC 6822, present some of the strongest observational support for a flat core at the center of galactic dark matter (DM) halos. We use detailed, cosmologically motivated numerical models to investigate the systematic effects and the accuracy of recovering parameters of the galaxies. Some of our models match the observed structure of the two galaxies remarkably well. Our analysis shows that the rotation curves of these two galaxies are instead quite compatible with their DM halos having steep cuspy density profiles. The rotation curves in our models are measured using standard observational techniques, projecting velocities along the line of sight of an imaginary observer and performing a tilted-ring analysis. The models reproduce the rotation curves of both galaxies and the disk surface brightness profiles, as well as the profile of isophotal ellipticity and position angle. The models are centrally dominated by baryons; however, the DM component is globally dominant. The simulated disk mass is marginally consistent with a stellar mass-to-light ratio, in agreement with the observed colors and the detected gaseous mass. We show that noncircular motions, combined with gas pressure support and projection effects, result in a large underestimation of the circular velocity in the central ~1 kpc region, creating the illusion of a constant-density core. Although the systematic effects mentioned above are stronger in barred systems, they are also present in axisymmetric disks. Our results strongly suggest that there is no contradiction between the observed rotation curves in dwarf galaxies and the cuspy central DM density profiles predicted by cold dark matter models.

Mass loss from dwarf spheroidal galaxies: the origins of shallow dark matter cores and exponential surface brightness profiles

Dwarf spheroidal galaxies have shallow central dark matter density profiles, low angular momentum and approximately exponential surface brightness distributions. Through N-body simulations and analytic calculations we investigate the extent to which these properties can be generated from ``typical'' $\Lambda$CDM galaxies, which differ in all of these properties, by the dynamical consequences of feedback. We find that, for a wide range of initial conditions, one impulsive mass loss event will naturally produce a surface brightness profile in the remaining stellar component of a dwarf spheroidal galaxy (dSph) which is well fit over many scale lengths by an exponential, in good qualitative agreement with observations of Local Group dSphs. Furthermore, two impulsive mass loss phases, punctuated by significant gas re-accretion, are found to be sufficient to transform a central density cusp in the dark matter profile into a near-constant density core. This may then provide the missing link between current cosmological simulations, which predict a central cusp in the dark matter density profile, and current observations, which find much shallower central density profiles. We also look at the angular momentum history of dSphs and demonstrate that if these galaxies have spent most of their lifetime in tidal isolation from massive galaxies then they cannot have formed from high angular momentum gas discs.

Off‐Axis Cluster Mergers: Effects of a Strongly Peaked Dark Matter Profile

We present a parameter study of offset mergers between clusters of galaxies. Using the Eulerian hydrodynamics/N-body code COSMOS, we simulate mergers between nonisothermal, hydrostatic clusters with a steep central dark matter density profile and a β-model gas profile. We constrain global properties of the model clusters using observed cluster statistical relationships. We consider impact parameters between 0 and 5 times the dark matter scale radius and mass ratios of 1 : 1 and 1 : 3. The morphological changes, relative velocities, and temperature jumps we observe agree with previous studies using the King profile for the dark matter. We observe a larger jump in X-ray luminosity (~4-10 times) than in previous work, and we argue that this increase is most likely a lower limit due to our spatial resolution. We emphasize that luminosity and temperature jumps due to mergers may have an important bearing on constraints on Ω derived from the observation of hot clusters at high redshift. Shocks are relatively weak in the cluster cores; hence, they do not significantly increase the entropy there. Instead, shocks create entropy in the outer regions, and this high-entropy gas is mixed with the core gas during later stages of the merger. Ram pressure initiates mixing by displacing the core gas from its potential center, causing it to become convectively unstable. The resulting convective plumes produce large-scale turbulent motions with eddy sizes up to several hundred kiloparsecs. This turbulence is pumped by dark matter-driven oscillations in the gravitational potential. Even after nearly a Hubble time these motions persist as subsonic turbulence in the cluster cores, providing 5%-10% of the support against gravity. The dark matter oscillations are also reflected in the extremely long time following a merger required for the remnant to reach virial equilibrium.