Dark Matter Density Profile Research Articles

Statistical strong lensing

Context. The number of known strong gravitational lenses is expected to grow substantially in the next few years. The combination of large samples of lenses has the potential to provide strong constraints on the inner structure of galaxies. Aims. We investigate the extent to which we can calibrate stellar mass measurements and constrain the average dark matter density profile of galaxies by combining strong lensing data from thousands of lenses. Methods. We generated mock samples of axisymmetric lenses. We assume that, for each lens, we have measurements of two image positions of a strongly lensed background source, as well as magnification information from full surface brightness modelling, and a stellar-population-synthesis-based estimate of the lens stellar mass. We then fitted models describing the distribution of the stellar population synthesis mismatch parameter αsps (the ratio between the true stellar mass and the stellar-population-synthesis-based estimate) and the dark matter density profile of the population of lenses to an ensemble of 1000 mock lenses. Results. We obtain the average αsps, projected dark matter mass, and dark matter density slope with greater precision and accuracy compared with current constraints. A flexible model and knowledge of the lens detection efficiency as a function of image configuration are required in order to avoid a biased inference. Conclusions. Statistical strong lensing inferences from upcoming surveys provide a way to calibrate stellar mass measurements and to constrain the inner dark matter density profile of massive galaxies.

The MUSE-Faint survey. II. The dark matter-density profile of the ultra-faint dwarf galaxy Eridanus 2

Aims. We use stellar line-of-sight velocities to constrain the dark-matter density profile of Eridanus 2, an ultra-faint dwarf galaxy with an absolute V-band magnitude MV = −7.1 that corresponds to a stellar mass M* ≈ 9 × 104 M⊙. We furthermore derive constraints on fundamental properties of self-interacting and fuzzy dark matter scenarios. Methods. We present new observations of Eridanus 2 from MUSE-Faint, a survey of ultra-faint dwarf galaxies with the Multi Unit Spectroscopic Explorer on the Very Large Telescope, and determine line-of-sight velocities for stars inside the half-light radius. Combined with literature data, we have 92 stellar tracers out to twice the half-light radius. With these tracers we constrain models of cold dark matter, self-interacting dark matter, and fuzzy dark matter, using CJAM and pyGravSphere for the dynamical analysis. The models of self-interacting and fuzzy dark matter relate the density profile to the self-interaction coefficient and the dark-matter particle mass, respectively. Results. We find substantial evidence (Bayes factor ∼10−0.6) for cold dark matter (a cuspy halo) over self-interacting dark matter (a cored halo) and weak evidence (Bayes factor ∼10−0.4) for fuzzy dark matter over cold dark matter. We find a virial mass M200 ∼ 108 M⊙ and astrophysical factors J(αcJ) ~ 1011 M⊙2 kpc−5 and D(αcD) ~ 102 − 102.5 M⊙ kpc−2 (proportional to dark-matter annihilation and decay signals, respectively), the exact values of which depend on the density profile model. The mass-to-light ratio within the half-light radius is consistent with the literature. We do not resolve a core (rc < 47 pc, 68% confidence level) or a soliton (rsol < 7.2 pc, 68% confidence level). These limits are equivalent to an effective self-interaction coefficient fΓ < 2.2 × 10−29 cm3 s−1 eV−1 c2 and a fuzzy-dark-matter particle mass ma > 4.0 × 10−20 eV c−2. The constraint on self-interaction is complementary to those from gamma-ray searches. The constraint on fuzzy-dark-matter particle mass is inconsistent with those obtained for larger dwarf galaxies, suggesting that the flattened density profiles of those galaxies are not caused by fuzzy dark matter.

How baryons can significantly bias cluster count cosmology

ABSTRACT We quantify two main pathways through which baryonic physics biases cluster count cosmology. We create mock cluster samples that reproduce the baryon content inferred from X-ray observations. We link clusters to their counterparts in a dark matter-only universe, whose abundances can be predicted robustly, by assuming the dark matter density profile is not significantly affected by baryons. We derive weak lensing halo masses and infer the best-fitting cosmological parameters Ωm, S8 = σ8(Ωm/0.3)0.2, and w0 from the mock cluster sample. We find that because of the need to accommodate the change in the density profile due to the ejection of baryons, weak lensing mass calibrations are only unbiased if the concentration is left free when fitting the reduced shear with NFW profiles. However, even unbiased total mass estimates give rise to biased cosmological parameters if the measured mass functions are compared with predictions from dark matter-only simulations. This bias dominates for haloes with $m_\mathrm{500c} \lt 10^{14.5} \, \rm h^{-1} \, \mathrm{M_\odot }$. For a stage IV-like cluster survey without mass estimation uncertainties, an area $\approx 15\,000 \, \mathrm{deg^2}$ and a constant mass cut of $m_\mathrm{200m,min} = 10^{14} \,\rm h^{-1} \, \mathrm{M_\odot }$, the biases are $-11 \pm 1 \, \mathrm{per\, cent}$ in Ωm, $-3.29 \pm 0.04 \, \mathrm{per\, cent}$ in S8, and $9 \pm 1.5 \, \mathrm{per\, cent}$ in w0. The statistical significance of the baryonic bias depends on how accurately the actual uncertainty on individual cluster mass estimates is known. We suggest that rather than the total halo mass, the (re-scaled) dark matter mass inferred from the combination of weak lensing and observations of the hot gas, should be used for cluster count cosmology.

Robust limits from upcoming neutrino telescopes and implications on minimal dark matter models

Experimental developments in neutrino telescopes are drastically improving their ability to constrain the annihilation cross-section of dark matter. In this paper, we employ an angular power spectrum analysis method to probe the galactic and extra-galactic dark matter signals. First we derive projections for a next generation of neutrino telescope that is inspired by KM3NeT. We emphasise that such analysis is much less sensitive to the choice of dark matter density profile. Remarkably, the projected sensitivity is improved by more than an order of magnitude with respect to the existing limits obtained by assuming the Burkert dark matter density profile describing the galactic halo.Second, we analyse minimal extensions to the Standard Model that will be maximally probed by the next generation of neutrino telescopes. As benchmark scenarios, we consider Dirac dark matter in s- and t-channel models with vector and scalar mediators. We follow a global approach by examining all relevant complementary experimental constraints.We find that neutrino telescopes will be able to competitively probe significant portions of parameter space. Interestingly, the anomaly-free L_μ-L_τ model can potentially be explored in regions where the relic abundance is achieved through freeze-out mechanism.

Minimally deformed wormholes

This work is devoted to the study of wormhole solutions in the framework of gravitational decoupling by means of the minimal geometric deformation scheme. As an example, to analyze how this methodology works in this scenario, we have minimally deformed the well-known Morris–Thorne model. The decoupler function f(r) and the theta -sector are determined considering the following approaches: (i) the most general linear equation of state relating the theta _{mu nu } components is imposed and (ii) the generalized pseudo-isothermal dark matter density profile is mimicked by the temporal component of the theta -sector. It is found that the first approach leads to a non-asymptotically flat space-time with an unbounded mass function. To address this issue we have matched both the wormhole and the Schwarzschild vacuum solutions, via a thin-shell at the junction surface. Using the second approach, it can be seen that, on one hand, the solution for gamma =1 does not give place to a bounded mass and it presents a topological defect at large distances; on the other hand, the wormhole manifold is asymptotically flat in the gamma =2 case. In order to satisfy the flare-out condition, we have found restrictions on the value of the alpha parameter, which is related with the amount of exotic matter distribution. Finally, the averaged weak energy condition has been analyzed by using the volume integral quantifier.

High energy window for probing dark matter with cosmic-ray antideuterium and antihelium * *Supported in part by the National Key R&D Program of China (2017YFA0402204) and by the National Natural Science Foundation of China (NSFC) (11825506, 11821505, U1738209, 11851303, 11947302)

Cosmic-ray (CR) anti-nuclei are often considered important observables for indirect dark matter (DM) detection at low kinetic energies, below GeV per nucleon. Since the primary CR fluxes drop quickly towards high energies, the secondary anti-nuclei in CR are expected to be significantly suppressed in high energy regions (gtrsim 100 GeV per nucleon). If DM particles are heavy, the annihilation productions of DM can be highly boosted, and thus the fluxes of anti-nuclei produced by DM annihilation may exceed the secondary background at high energies, which opens a high energy window for indirect DM detection. We investigate the possibility of detecting heavy DM particles which annihilate into high energy anti-nuclei. We use the Monte Carlo generators PYTHIA, EPOS-LHC and DPMJET and the coalescence model to simulate the production of anti-nuclei, and constrain the DM annihilation cross-sections by using the AMS-02 and HAWC antiproton data and the HESS galactic center gamma -ray data. We find that the conclusion depends on the choice of DM density profiles. For the “Cored” type profile with a DM particle mass gtrsim 10 TeV, the contributions from DM annihilation can exceed the secondary background in high energy regions, which opens the high energy window, while for the “Cuspy” type profile, the excess disappears.

Atacama Cosmology Telescope: Combined kinematic and thermal Sunyaev-Zel’dovich measurements from BOSS CMASS and LOWZ halos

The scattering of cosmic microwave background (CMB) photons off the free-electron gas in galaxies and clusters leaves detectable imprints on high resolution CMB maps: the thermal and kinematic Sunyaev-Zel'dovich effects (tSZ and kSZ respectively). We use combined microwave maps from the Atacama Cosmology Telescope (ACT) DR5 and Planck in combination with the CMASS and LOWZ galaxy catalogs from the Baryon Oscillation Spectroscopic Survey (BOSS DR10 and DR12), to study the gas associated with these galaxy groups. Using individual reconstructed velocities, we perform a stacking analysis and reject the no-kSZ hypothesis at 6.5$\sigma$, the highest significance to date. This directly translates into a measurement of the electron number density profile, and thus of the gas density profile. Despite the limited signal to noise, the measurement shows at high significance that the gas density profile is more extended than the dark matter density profile, for any reasonable baryon abundance (formally $>90\sigma$ for the cosmic baryon abundance). We simultaneously measure the tSZ signal, i.e. the electron thermal pressure profile of the same CMASS objects, and reject the no-tSZ hypothesis at 10$\sigma$. We combine tSZ and kSZ measurements to estimate the electron temperature to 20% precision in several aperture bins, and find it comparable to the virial temperature. In a companion paper, we analyze these measurements to constrain the gas thermodynamics and the properties of feedback inside galaxy groups. We present the corresponding LOWZ measurements in this paper, ruling out a null kSZ (tSZ) signal at 2.9 (13.9)$\sigma$, and leave their interpretation to future work. Our stacking software ThumbStack is publicly available at https://github.com/EmmanuelSchaan/ThumbStack and directly applicable to future Simons Observatory and CMB-S4 data.

The dynamical structure of broken power-law and double power-law models for dark matter haloes

ABSTRACT Galaxy kinematics and gravitational lensing are two complementary ways to constrain the distribution of dark matter on galaxy scales. The typical dark matter density profiles adopted in dynamical studies cannot easily be adopted in lensing studies. Ideally, a mass model should be used that has the global characteristics of realistic dark matter distributions, and that allows for an analytical calculation of the magnifications and deflection angles. A simple model with these properties, the broken power-law (BPL) model, has very recently been introduced. We examine the dynamical structure of the family of BPL models. We derive simple closed expressions for basic dynamical properties, and study the distribution function under the assumption of velocity isotropy. We find that none of the BPL models with realistic parameters has an isotropic distribution function that is positive over the entire phase space, implying that the BPL models cannot be supported by an isotropic velocity distribution, or models with a more radially anisotropic orbital structure. This result limits the attractiveness of the BPL family as a tool for lensing studies to some degree. More generally, we find that not all members of the general family of double power-law or Zhao models, often used to model dark matter haloes, can be supported by an isotropic or radially anisotropic distribution function. In other words, the distribution function may become negative even for spherically symmetric models with a well-behaved density profile.

Testing the ALP-photon coupling with polarization measurements of Sagittarius A⋆

Ultra-light bosons such as axions or axion-like particles (ALPs), are promising candidates to solve the dark matter problem. A unique way to detect such ALPs is to search for the periodic oscillation feature of the position angles of linearly polarized photons emitted from the galaxy center. In this work, we use the high-resolution polarimetric measurements of the radiation near the super-massive black hole (SMBH) in the center of the Milky Way, i.e., Sagittarius A⋆ (Sgr A⋆), by a sub-array of the Event Horizon Telescope to search for the ultra-light ALPs. We derive upper limits on the ALP-photon coupling of ∼ 10-12 GeV-1 for ALP masses of ma∼ (10-19-10-18) eV, with a solitonic core + NFW dark matter density profile. Our results are stronger than that derived from the observations of SN1987A and a population of supernovae in the mass window of (10-19-10-17) eV. Improved polarimetric measurements with the full Event Horizon Telescope can further strengthen the constraints.

Observational insights on the origin of giant low surface brightness galaxies

ABSTRACT Giant low surface brightness galaxies (gLSBGs) with dynamically cold stellar discs reaching the radius of 130 kpc challenge currently considered galaxy formation mechanisms. We analyse new deep long-slit optical spectroscopic observations, archival optical images, and published Hi and optical spectroscopic data for a sample of seven gLSBGs, for which we performed mass modelling and estimated the parameters of dark matter haloes assuming the Burkert dark matter density profile. Our sample is not homogeneous by morphology, parameters of stellar populations, and total mass, however, six of seven galaxies sit on the high-mass extension of the baryonic Tully–Fisher relation. In UGC 1382, we detected a global counterrotation of the stellar high surface brightness (HSB) disc with respect to the extended LSB disc. In UGC 1922 with signatures of a possible merger, the gas counterrotation is seen in the inner disc. Six galaxies host active galactic nuclei, three of which have the estimated black hole masses substantially below those expected for their (pseudo-)bulge properties suggesting poor merger histories. Overall, the morphology, internal dynamics, and low star formation efficiency in the outer discs indicate that the three formation scenarios shape gLSBGs: (i) a two-stage formation when an HSB galaxy is formed first and then grows an LSB disc by accreting gas from an external supply; (ii) an unusual shallow and extended dark matter halo; (iii) a major merger with fine-tuned orbital parameters and morphologies of the merging galaxies.

On the origin of the gamma-ray emission from Omega Centauri: millisecond pulsars and dark matter annihilation

We explore two possible scenarios to explain the observed γ-ray emission associated with the atypical globular cluster ω-Centauri: emission from millisecond pulsars (MSP) and dark matter (DM) annihilation. In the first case we predict the total number of MSPs in the globular cluster (n=45+22−16) using a new Bayesian method that combines the observational uncertainty in γ-ray counts with the intrinsic variation in individual pulsar luminosities. A DM interpretation is motivated by the possibility of ω-Centauri being the remnant core of an ancient dwarf galaxy hosting a surviving DM component. At least two annihilation channels, light quarks and muons, can plausibly produce the observed γ-ray spectrum. We are able to constrain the DM particle mass despite substantial uncertainties in the shape of the density profile (10 GeV ≲ mχ ≲ 30 GeV for annihilation into light quarks and 5 GeV ≲ mχ ≲ 9 GeV for annihilation into muons). We translate upper limits on ω-Centauri's remnant dark matter content into lower limits on the annihilation cross section (⟨ σ v⟩ ≳ 10−29 cm3 s −1 and ⟨ σ v⟩ ≳ 10−28 cm3 s −1 for quarks and muons respectively), taking into account the spatial extension of the DM halo. Moreover, there is a relatively small range of DM density profiles which are consistent with ω-Centauri's kinematics and stellar mass and can explain its γ-ray spectrum while simultaneously evading CMB constraints on dark matter annihilation. Further analysis of ω-Centauri's internal kinematics, and/or additional information on the resident MSP population will yield much stronger constraints and shed light about the origin of this otherwise mysterious γ-ray source.

An interpretation of a simple portal dark matter model on Fermi-LAT gamma-ray excess

Dark matter is one of the main components of the universe. Due to its weak interaction with other particles, dark matter cannot be identified as a particle that we know of. We are interested in a simple particle physics scenario where dark matter is identified with the fermion in the dark sector and the standard model sector is connected to dark matter via the portal scalar field. One of the promising signals from these models are gamma-rays from dark matter annihilation processes. In 2016, the Fermi-LAT collaboration detected a gamma-ray excess signal coming from Milky Way’s galactic center which was immediately regarded as a possible candidate for the first detection of dark matter. In this project, we study an interpretation of the signal from Fermi-LAT as a dark matter annihilation from portal dark matter model. First, we calculated gamma-ray fluxes from dark matter annihilations as subsequent decays of portal scalars where the astrophysical factor is calculated from the Navarro-Frenk-White (NFW) dark matter density profile. We found that the simplest model does not fit adequately with chi-squared per degree of freedom, . We proposed that a part of the Fermi-LAT excess might come from another source of gamma-ray. The dark matter model combined with an unknown astrophysical source is then studied. The combined model is able to provide a reasonable fit indicating that scalar mass is 130 GeV, where dark matter mass is in the range of 150 − 350 GeV and 〈σν〉 is around 7 × 10−26 cm3/s.

Effect comparison of dark matter annihilation pressure to NFW and pseudo-isothermal profiles of low surface brightness galaxies

We have studied the effect of gas pressure created by electrons and positrons produced from dark matter annihilation for low surface brightness (LSB) galaxies. We have applied 4 different gas and stellar disk models and 2 different dark matter density profiles, i.e. Navarro Frenk and White (NFW) and pseudo-isothermal, to each galaxy. We assume that electrons and positrons are produced from dark matter annihilation and they can lose their energy to photons and the interstellar medium in the galaxies by different loss processes. The pressure of electron and positron gas is a function of the electron-positron spectrum obtained from a diffusion-loss equation which included source term, diffusion coefficient and loss rate. We have added the pressure gradient to the rotation curves of LSB galaxies. We have compared the results with observations by using reduced chi-square. We have found that the pressure from dark matter annihilation provided better fits for several galaxies for NFW profiles but it doesn’t play any role for pseudo-isothermal profiles. From these results, we can use NFW profile with pressure from dark matter annihilation to improve the situation of cusp-core problems and to constrain properties of dark matter particles by rotation curves of LSB galaxies for future studies.

Velocity-dependent self-interacting dark matter from groups and clusters of galaxies

We probe the self-interactions of dark matter with relaxed galaxy groups and clusters using observational data from strong and weak lensing and stellar kinematics. Our analysis uses the Jeans formalism and considers a wider range of systematic effects than in previous work, including adiabatic contraction and stellar anisotropy, to robustly constrain the self-interaction cross section. For both groups and clusters, our results show a mild preference for a nonzero cross section compared with cold collisionless dark matter. Our groups result, σ/m=0.5±0.2 cm2/g, places the first constraint on self-interacting dark matter (SIDM) at an intermediate scale M200∼ 1014 M⊙ between galaxies and massive clusters. For massive clusters with M200∼ 1015 M⊙, our result is σ/m=0.19±0.09 cm2/g, with an upper limit of σ / m < 0.35 cm2/g (95% CL) . Thus, our results disfavor a velocity-independent cross section of order 1 cm2/g or larger needed to impact small scale structure problems in galaxies, but are consistent with a velocity-dependent cross section that decreases with increasing scattering velocity. Comparing the cross sections with and without the effect of adiabatic contraction, we find that adiabatic contraction produces slightly larger values for our data sample, but they are consistent at the 1σ level. Finally, to validate our approach, we apply our Jeans analysis to a sample of mock data generated from SIDM-plus-baryons simulations with σ/m = 1 cm2/g. This is the first test of the Jeans model at the level of stellar and lensing observables directly measured from simulations. We find our analysis gives a robust determination of the cross section, as well as consistently inferring the true baryon and dark matter density profiles.

From dwarf galaxies to galaxy clusters: Self-Interacting Dark Matter over 7 orders of magnitude in halo mass

In this paper we study the density profiles of self-interacting dark matter (SIDM) haloes spanning the full observable mass range, from dwarf galaxies to galaxy clusters. Using realistic simulations that model the baryonic physics relevant for galaxy formation, we compare the density profiles of haloes simulated with either SIDM or cold and collisionless dark matter (CDM) to those inferred from observations of stellar velocity dispersion, gas rotation curves, weak and strong gravitational lensing, and/or X-ray maps. We make our comparison in terms of the maximal surface density of haloes, circumventing the need for semi-analytic or parametric models for dark matter density profiles. We find that the maximal surface density as a function of halo mass is well reproduced by CDM simulations that include baryons, while for SIDM with a velocity-independent cross-section of 1 cm2/g, the simulated galaxy clusters have mean maximal surface densities that are below those of observed systems by an amount greater than the standard deviation of the observed maximal surface density at fixed mass. For less massive systems both CDM and SIDM agree with the observation equally well.

Equilibrium axisymmetric halo model for the Milky Way and its implications for direct and indirect dark matter searches

We for the first time provide self-consistent axisymmetric phase-space distribution models for the Milky Way's dark matter (DM) halo which are carefully matched against the latest kinematic measurements through Bayesian analysis. By using broad priors on the individual galactic components, we derive conservative estimates for the astrophysical factors entering the interpretation of direct and indirect DM searches. While the resulting DM density profiles are in good agreement with previous studies, implying $\rho_\odot \approx 10^{-2} \, M_\odot / \mathrm{pc}^3$, the presence of baryonic disc leads to significant differences in the local DM velocity distribution in comparison with the standard halo model. For direct detection, this implies roughly 30% stronger cross-section limits at DM masses near detectors maximum sensitivity and up to an order of magnitude weaker limits at the lower end of the mass range. Furthermore, by performing Monte-Carlo simulations for the upcoming DARWIN and DarkSide-20k experiments, we demonstrate that upon successful detection of heavy DM with coupling just below the current limits, the carefully constructed axisymmetric models can eliminate bias and reduce uncertainties by more then 50% in the reconstructed DM coupling and mass, but also help in a more reliable determination of the scattering operator. Furthermore, the velocity anisotropies induced by the baryonic disc can lead to significantly larger annual modulation amplitude and sizable differences in the directional distribution of the expected DM-induced events. For indirect searches, we provide the differential $J$-factors and compute several moments of the relative velocity distribution that are needed for predicting the rate of velocity-dependent annihilations. However, we find that accurate predictions are still hindered by large uncertainties regarding the DM distribution near the galactic center.

The surprising accuracy of isothermal Jeans modelling of self-interacting dark matter density profiles

ABSTRACT Recent claims of observational evidence for self-interacting dark matter (SIDM) have relied on a semi-analytic method for predicting the density profiles of galaxies and galaxy clusters containing SIDM. We present a thorough description of this method, known as isothermal Jeans modelling, and then test it with a large ensemble of haloes taken from cosmological simulations. Our simulations were run with cold and collisionless dark matter (CDM) as well as two different SIDM models, all with dark matter only variants as well as versions including baryons and relevant galaxy formation physics. Using a mix of different box sizes and resolutions, we study haloes with masses ranging from 3 × 1010 to $3 \times 10^{15} \mathrm{\, M_\odot }$. Overall, we find that the isothermal Jeans model provides as accurate a description of simulated SIDM density profiles as the Navarro–Frenk–White profile does of CDM haloes. We can use the model predictions, compared with the simulated density profiles, to determine the input DM–DM scattering cross-sections used to run the simulations. This works especially well for large cross-sections, while with CDM our results tend to favour non-zero (albeit fairly small) cross-sections, driven by a bias against small cross-sections inherent to our adopted method of sampling the model parameter space. The model works across the whole halo mass range we study, although including baryons leads to DM profiles of intermediate-mass ($10^{12} - 10^{13} \mathrm{\, M_\odot }$) haloes that do not depend strongly on the SIDM cross-section. The tightest constraints will therefore come from lower and higher mass haloes: dwarf galaxies and galaxy clusters.

The eccentricity enhancement effect of intermediate-mass-ratio-inspirals: dark matter and black hole mass * *Supported by National Natural Science Foundation of China (11503078, 11573060, 11673060, 11661161010)

It was found that dark matter (DM) in an intermediate-mass-ratio-inspiral (IMRI) system has a significant enhancement effect on the orbital eccentricity of a stellar massive compact object, such as a black hole (BH), which may be tested by space-based gravitational wave (GW) detectors, including LISA, Taiji, and Tianqin in future observations. In this paper, we study the enhancement effect of the eccentricity for an IMRI under different DM density profiles and center BH masses. Our results are as follows: (1) in terms of the general DM spike distribution, the enhancement of the eccentricity is basically consistent with the power-law profile, which indicates that it is reasonable to adopt the power-law profile; (2) in the presence of a DM spike, the different masses of the center BH will affect the eccentricity, which provides a new way for us to detect the BH's mass; and (3) considering the change in the eccentricity in the presence and absence of a DM spike, we find that it is possible to distinguish DM models by measuring the eccentricity at a scale of approximately .

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.

Investigating the Fermi Large Area Telescope sensitivity of detecting the characteristics of the Galactic center excess

The center of the Milky Way is offering one of the most striking mysteries in astroparticle physics. An excess of $\ensuremath{\gamma}$ rays (GCE) has been measured by several groups in the data collected by the Fermi Large Area Telescope (LAT) toward the Galactic center region. The spectrum and spatial morphology of the GCE have been claimed by some groups to be compatible with a signal from the galactic halo of dark matter (DM). Instead, other analyses have demonstrated that the GCE properties, e.g., its energy spectrum, highly depend on the choice of the galactic interstellar emission (IEM) model source catalogs and analysis techniques. In this paper, we investigate the sensitivity of Fermi LAT to detect the characteristics of the GCE. In particular, we simulate the GCE as given by DM, and we verify that, with a perfect knowledge of the background components, its energy spectrum, position, spatial morphology, and symmetry is properly measured. We also inspect two more realist cases for which there are imperfections in the IEM model. In the first, we have an unmodeled $\ensuremath{\gamma}$-ray source, constituted by the low-latitude component of the Fermi bubbles. In the second, we simulate the data with one IEM template and analyze the data with another. We verify that a mismodeling of the IEM introduces a systematics of about 10--15% in the GCE energy spectrum between 1--10 GeV and about 5% in the value of the slope for a Navarro-Frenk-White DM density profile, which is used to fit the GCE spatial morphology. Finally, we show how the GCE would be detected in case of alternative processes such as $\ensuremath{\gamma}$-ray emission from a bulge population of pulsars or from electrons and positrons or protons injected from the Galactic center. We demonstrate that for each of these cases, there is a distinctive smoking gun signature that would help to identify the real mechanism behind the origin of the GCE.