Dark Matter Halo Profile Research Articles

Orbit-based dynamical models of the Sculptor dSph galaxy

We have developed spherically symmetric dynamical models of dwarf spheroidal (dSph) galaxies using Schwarzschild's orbit superposition method. This type of modelling yields constraints both on the total mass distribution (e.g. enclosed mass and scale radius) and on the orbital structure of the system (e.g. velocity anisotropy). This method is thus less prone to biases introduced by assumptions in comparison to the more commonly used Jeans modelling, and it allows us to put reliable constraints on their dark matter content. Here we present our results for the Sculptor dSph galaxy, after testing our methods on mock data sets. We fit both the second and fourth velocity moment profiles to break the mass–anisotropy degeneracy. For an Navarro, Frenk & White (NFW) dark matter halo profile, we find that the mass of Sculptor within 1 kpc is M1 kpc = (1.03 ± 0.07) × 108 M⊙, and that its velocity anisotropy profile is tangentially biased and nearly constant for radii beyond ∼100 pc. The preferred concentration (c ∼ 15) is low for its dark matter mass but consistent within the scatter found in N-body cosmological simulations. When we let the value of the central logarithmic slope α vary, we find that the best-fitting model has α = 0, although an NFW cusp or shallower is consistent at the 1σ confidence level. On the other hand, very cuspy density profiles with logarithmic central slopes α < −1.5 are strongly disfavoured for Sculptor.

The Dark Matter halo of the Milky Way, AD 2013

We derive the mass model of the Milky Way (MW), crucial for Dark Matter (DM) direct and indirectdetection, using recent data and a cored dark matter (DM) halo profile, which is favoured by studiesof external galaxies.The method used consists in fitting a spherically symmetric model of the Galaxy with a Burkert DMhalo profile to available data: MW terminal velocities in the region inside the solar circle,circular velocity as recently estimated from maser star forming regions at intermediate radii, andvelocity dispersions of stellar halo tracers for the outermost Galactic region. The latter arereproduced by integrating the Jeans equation for every modeled mass distribution, and by allowingfor different velocity anisotropies for different tracer populations.For comparison we also consider a Navarro-Frenk-White profile. We find that the cored profile isthe preferred one, with a shallow central density of ρH ∼ 4 × 107M☉/kpc3 and a largecore radius RH ∼ 10 kpc, as observed in external spirals and in agreement with the mass modelunderlying the Universal Rotation Curve of spirals.We describe also the derived model uncertainties, which are crucially driven by the poorlyconstrained velocity dispersion anisotropies of halo tracers.The emerging cored DM distribution has implications for the DM annihilation angular profile, whichis much less boosted in the Galactic center direction with respect to the case of the standardΛCDM, NFW profile. Using the derived uncertainties we discuss finally the limitations andprospects to discriminate between cored and cusped DM profile with a possible observed diffuse DMannihilation signal.The present mass model aims to characterize the present-day description of the distribution ofmatter in our Galaxy, which is needed to frame current crucial issues of Cosmology, Astrophysics andElementary Particles.

Composite millicharged dark matter

We study a composite millicharged dark matter model. The dark matter is in the form of pion-like objects emerging from a higher scale QCD-like theory. We present two distinct possibilities with interesting phenomenological consequences based on the choice of the parameters. In the first one, the dark matter is produced non-thermally and it could potentially account for the 130 GeV Fermi photon line via decays of the "dark pions". We estimate the self-interaction cross section which might play an important role both in changing the dark matter halo profile at the center of the galaxy and in making the dark matter warmer. In the second version the dark matter is produced via the freeze-in mechanism. Finally we impose all possible astrophysical, cosmological and experimental constraints. We study in detail generic constraints on millicharged dark matter that can arise from anomalous isotope searches of different elements and we show why constraints based on direct searches from underground detectors are not generally valid.

The 111 and 129 GeVγ-ray lines from annihilations in the Milky Way dark matter halo, dark disk and subhalos

Recently a series of indications have been put forward suggesting the presence of two -ray lines at 110-130 GeV (centered at 111 and 129 GeV). Signals of these lines have been observed toward the Galactic center, at some galaxy clusters and among some of the unassociated point sources of the 2 years Fermi catalogue. Such a combination of signals could be generated by dark matter annihilations in the main dark matter halo, its substructures and nearby galaxy clusters. We discuss in this work the consistency between the number of events observed at the line energies in the sky and the predictions using results from the Via Lactea II numerical simulation and extrapolations below its mass resolution, taking into account that the annihilation cross-section to the lines can be estimated from the Galactic center signal. We find that some extrapolations to small substructures can naturally account for the point sources signal, although the hypothesis of background only cannot be rejected. We also study the morphology of the -ray sky at the 2 lines energies, testing different Galactic diffuse background models to account for interstellar medium uncertainties and different assumptions on the DM diffuse component profile. We find from template fits that within reasonable diffuse background uncertainties the presence of a spherical halo component is preferred with cuspier dark matter halo profiles being preferable even from the full sky fit. We finally check the impact of a dark disk component suggested by cosmological simulations that include baryons and find that thin dark disks can not be disfavored, thus possibly accounting for the preferentially closer to the Galactic disk distribution of the point sources lines signal.

Fitting functions for dark matter density profiles

We present a unified parameterization of the fitting functions suitable for density profiles of dark matter haloes or elliptical galaxies. A notable feature is that the classical Einasto profile appears naturally as the continuous limiting case of the cored subfamily amongst the double power-law profiles of Zhao (1996). Based on this, we also argue that there is basically no qualitative difference between halo models well-fitted by the Einasto profile and the standard NFW model. This may even be the case quantitatively unless the resolutions of simulations and the precisions of fittings are sufficiently high to make meaningful distinction possible.

Effect of small-scale density perturbations on the formation of dark matter halo profiles

Abstract With the help of a set of toy N-body models of dark halo formation, we study the impact of small-scale initial perturbations on the inner density profiles of haloes. We find a significant flattening of the inner slope to α=−0.5 in some range of scales and amplitudes of the perturbations (while in the case of absence of these perturbations, the Navarro–Frenk–White profile with α=−1 is reproduced). This effect may be responsible for the formation of cuspless galactic haloes.

Astronomical constraints on quantum theories of cold dark matter – I. Einasto density profile for galactic haloes

Among different models of dark matter, the so-called quantum (or ‘fuzzy’) cold dark matter plays an important role as it allows removing cuspy halo profiles and an abundance of low mass haloes, which are predicted by cold dark matter models but have never been observed. The basic idea of the quantum cold dark matter is the existence of extremely light bosonic particles whose expected masses are of the order of 10−22 eV or even as small as 10−24 eV. With such a small mass, the particle's behaviour in galactic dark matter haloes is described by the Schrödinger equation with a gravitational potential term. In this paper, two previously introduced quantum models of dark matter are reconsidered and the probability densities predicted by these models are compared to the astronomically established density profiles of dark matter haloes of the Milky Way and a dwarf galaxy. By imposing these astronomical constraints on the quantum models, it is shown that the models do reproduce well the Einasto profile with index n ≈ 0.56. However, the models can neither account for the total masses and halo shapes of these two galaxies, nor other galaxies, using the same dark matter elementary particle. Possible improvements of the quantum models that could potentially remove this deficiency are discussed.

Optical-to-virial velocity ratios of local disc galaxies from combined kinematics and galaxy-galaxy lensing

In this paper, we measure the optical-to-virial velocity ratios Vopt/V200c of disk galaxies in the Sloan Digital Sky Survey (SDSS) at a mean redshift of <z> = 0.07 and with stellar masses 10^9 M_sun < M_* < 10^11 M_sun. Vopt/V200c, the ratio of the circular velocity measured at the virial radius of the dark matter halo (\sim150 kpc) to that at the optical radius of the disk (\sim10 kpc), is a powerful observational constraint on disk galaxy formation. It links galaxies to their dark matter haloes dynamically and constrains the total mass profile of disk galaxies over an order of magnitude in length scale. For this measurement, we combine Vopt derived from the Tully-Fisher relation (TFR) from Reyes et al. with V200c derived from halo masses measured with galaxy-galaxy lensing. In anticipation of this combination, we use similarly-selected galaxy samples for both the lensing and TFR analysis. For three M_* bins with lensing-weighted mean stellar masses of 0.6, 2.7, and 6.5 x 10^10 M_sun, we find halo-to-stellar mass ratios M_vir/M_* = 41, 23, and 26, with 1-sigma statistical uncertainties of around 0.1 dex, and Vopt/V200c = 1.27\pm0.08, 1.39\pm0.06, 1.27\pm0.08 (1{\sigma}). Our results suggest that the dark matter and baryonic contributions to the mass within the optical radius are comparable, if the dark matter halo profile has not been significantly modified by baryons. The results obtained in this work will serve as inputs to and constraints on disk galaxy formation models, which will be explored in future work. Finally, we note that this paper presents a new and improved galaxy shape catalogue for weak lensing that covers the full SDSS DR7 footprint.

A brief Review of the Scalar Field Dark Matter model

In the last time the cold dark matter (CDM) model has suggested more and more that it is not able to describe all the properties of nearby galaxies that can be observed in great detail as well as that it has some problems in the mechanism by which matter is more rapidly gathered into large-scale structure such as galaxies and clusters of galaxies. In this work we revisit an alternative model, the scalar field dark matter (SFDM) model, which proposes that the galactic haloes form by condensation of a scalar field (SF) very early in the Universe, i.e., in this model the haloes of galaxies are astronomical Bose-Einstein Condensate drops of SF. On the other hand, large-scale structures like clusters or superclusters of galaxies form similar to the ACDM model, by hierarchy, thus all the predictions of the ACDM model at cosmological scales are reproduced by SFDM. This model predicts that all galaxy haloes must be very similar and exist for higher redshifts than in the ACDM model. In the first part of this review we revisit the cosmological evolution of SFDM model with a scalar potential m2Φ2/2 + λΦ4/4 with two different frameworks: the field and fluid approach. We derive the evolution equations of the SF in the linear regime of perturbations as well. The scalar fluctuations have an oscillating growing mode and therefore, this kind of dark matter could lead to the early formation of gravitational structures in the Universe. We also revisit how BEC dark matter haloes exhibit a natural cut of the mass power spectrum. In the second part, we study the core central density profiles of BEC dark matter haloes and fit high-resolution rotation curves, we show a sample of some low surface brightness galaxies. The mean value of the logarithmic inner density slopes is α = −0.27 ± 0.18. Using a model independent new definition of the core in the BEC density profile, we show that the recent observation of the constant dark matter central surface density can be reproduced. We conclude that in light of the difficulties that the ΛCDM model is currently facing the SFDM model can be a worthy alternative to keep exploring further.

Effects of baryon mass loss on profiles of large galactic dark matter haloes

We perform controlled numerical experiments to asses the effect of baryon mass loss on the inner structure of large galactic dark matter haloes. This mass expulsion is intended to mimic both the supernovae and AGN feedbacks, as well as the evolution of stellar populations. This study is meant in particular for precursors of massive Early Type Galaxies, wherein strong AGN feedback (often dubbed "QSO mode" in galaxy formation models) has been proposed to remove on a short timescale, of the order of a few dynamical times, a substantial fraction of their baryons. In a previous paper we evaluated the observational consequences (size increase) of this process on the galactic structure (Ragone-Figueroa & Granato 2011). Here we focus on the distribution of dark matter in the galactic region. It is shown that the inner region of the DM halo expands and its density profile flattens by a sizeable amount, with little dependence on the expulsion timescale. We also evaluate the effect of the commonly made approximation of treating the baryonic component as a potential that changes in intensity without any variation in shape. This approximation leads to some underestimates of the halo expansion and its slope flattening. We conclude that cuspy density profiles in ETGs could be difficult to reconcile with an effective AGN (or stellar) feedback during the evolution of these systems.

Interacting dark matter contribution to the galactic 511 keV gamma ray emission: constraining the morphology with INTEGRAL/SPI observations

We compare the full-sky morphology of the 511 keV gamma ray excess measured by the INTEGRAL/SPI experiment to predictions of models based on dark matter (DM) scatterings that produce low-energy positrons: either MeV-scale DM that annihilates directly into e+e− pairs, or heavy DM that inelastically scatters into an excited state (XDM) followed by decay into e+e− and the ground state. By direct comparison to the data, we find that such explanations are consistent with dark matter halo profiles predicted by numerical many-body simulations for a Milky Way-like galaxy. Our results favor an Einasto profile over the cuspier NFW distribution and exclude decaying dark matter scenarios whose predicted spatial distribution is too broad. We obtain a good fit to the shape of the signal using six fewer degrees of freedom than previous empirical fits to the 511 keV data. We find that the ratio of flux at Earth from the galactic bulge to that of the disk is between 1.9 and 2.4, taking into account that 73% of the disk contribution may be attributed to the beta decay of radioactive 26Al.

Dwarf spheroidal galaxy kinematics and spiral galaxy scaling laws

Kinematic surveys of the dwarf spheroidal (dSph) satellites of the Milky Way are revealing tantalizing hints about the structure of dark matter (DM) haloes at the low-mass end of the galaxy luminosity function. At the bright end, modelling of spiral galaxies has shown that their rotation curves are consistent with the hypothesis of a universal rotation curve whose shape is supported by a cored dark matter halo. In this paper, we investigate whether the internal kinematics of the Milky Way dSphs are consistent with the particular cored DM distributions which reproduce the properties of spiral galaxies. Although the DM densities in dSphs are typically almost two orders of magnitude higher than those found in (larger) disc systems, we find consistency between dSph kinematics and Burkert DM haloes whose core radii r0 and central densities ρ0 lie on the extrapolation of the scaling law seen in spiral galaxies: log ρ0≃α log r0+ const with 0.9 < α < 1.1. We similarly find that the dSph data are consistent with the relation between ρ0 and baryon scalelength seen in spiral galaxies. While the origin of these scaling relations is unclear, the finding that a single DM halo profile is consistent with kinematic data in galaxies of widely varying size, luminosity and Hubble type is important for our understanding of observed galaxies and must be accounted for in models of galaxy formation.

Probing galaxy dark matter haloes in COSMOS with weak lensing flexion

Current theories of structure formation predict specific density profiles of galaxy dark matter haloes, and with weak gravitational lensing we can probe these profiles on several scales. On small scales, higher-order shape distortions known as flexion add significant detail to the weak lensing measurements. We present here the first detection of a galaxy-galaxy flexion signal in space-based data, obtained using a new Shapelets pipeline introduced here. We combine this higher-order lensing signal with shear to constrain the average density profile of the galaxy lenses in the Hubble Space Telescope COSMOS survey. We also show that light from nearby bright objects can significantly affect flexion measurements. After correcting for the influence of lens light, we show that the inclusion of flexion provides tighter constraints on density profiles than does shear alone. Finally we find an average density profile consistent with an isothermal sphere.

Conservative constraints on dark matter from the Fermi-LAT isotropic diffuse gamma-ray background spectrum

We examine the constraints on final state radiation from Weakly Interacting Massive Particle (WIMP) dark matter candidates annihilating into various standard model final states, as imposed by the measurement of the isotropic diffuse gamma-ray background by the Large Area Telescope aboard the Fermi Gamma-Ray Space Telescope. The expected isotropic diffuse signal from dark matter annihilation has contributions from the local Milky Way (MW) as well as from extragalactic dark matter. The signal from the MW is very insensitive to the adopted dark matter profile of the halos, and dominates the signal from extragalactic halos, which is sensitive to the low mass cut-off of the halo mass function. We adopt a conservative model for both the low halo mass survival cut-off and the substructure boost factor of the Galactic and extragalactic components, and only consider the primary final state radiation. This provides robust constraints which reach the thermal production cross-section for low mass WIMPs annihilating into hadronic modes. We also reanalyze limits from HESS observations of the Galactic Ridge region using a conservative model for the dark matter halo profile. When combined with the HESS constraint, the isotropic diffuse spectrum rules out all interpretations of the PAMELA positron excess based on dark matter annihilation into two lepton final states. Annihilation into four leptons through new intermediate states, although constrained by the data, is not excluded.

Leptonic dark matter annihilation in the evolving universe:constraints and implications

The cosmic electron and positron excesses have been explained aspossible dark matter (DM) annihilation products. In this work weinvestigate the possible effects of such a DM annihilation scenarioduring the evolution history of the Universe. We first calculate theextragalactic γ-ray background (EGRB), which is producedthrough the final state radiation of DM annihilation to chargedleptons and the inverse Compton scattering betweenelectrons/positrons and the cosmic microwave background. The DM haloprofile and the minimal halo mass, which are not yet well determinedfrom the current N-body simulations, are constrained by the EGRBdata from EGRET and Fermi telescopes. Then we discuss the impact ofsuch leptonic DM models on cosmic evolution, such as thereionization and heating of intergalactic medium, neutral Hydrogen21 cm signal and suppression of structure formation. We show thatthe impact on the Hydrogen 21 cm signal might show interestingsignatures of DM annihilation, but the influence on star formation isnot remarkable. Future observations of the 21 cm signals could beused to place new constraints on the properties of DM.

Testing adiabatic contraction with Sloan Digital Sky Survey elliptical galaxies

We study the profiles of 75 086 elliptical galaxies from the Sloan Digital Sky Survey (SDSS) at both large (50-500 kpc/h) and small (~3 kpc/h) scales. Weak lensing observations in the outskirts of the halo are combined with measurements of the stellar velocity dispersion in the interior regions of the galaxy for stacked galaxy samples. The weak lensing measurements are well characterized by a Navarro, Frenk and White (NFW) profile. The dynamical mass measurements exceed the extrapolated NFW profile even after the estimated stellar masses are subtracted, providing evidence for the modification of the dark matter profile by the baryons. This excess mass is quantitatively consistent with the predictions of the adiabatic contraction (AC) hypothesis. Our finding suggests that the effects of AC during galaxy formation are stable to subsequent bombardment from major and minor mergers. We explore several theoretical and observational systematics and conclude that they cannot account for the inferred mass excess. The most significant source of systematic error is in the IMF, which would have to increase the stellar mass estimates by a factor of two relative to masses from the Kroupa IMF to fully explain the mass excess without AC. Such an increase would create tension with results from SAURON (Cappellari et al. 2006). We demonstrate a connection between the level of contraction of the dark matter halo profile and scatter in the size-luminosity relation, which is a projection of the fundamental plane. Whether or not AC is the mechanism supplying the excess mass, models of galaxy formation and evolution must reconcile the observed halo masses from weak lensing with the comparatively large dynamical masses at the half light radii of the galaxies.

THE SUPERMASSIVE BLACK HOLE AND DARK MATTER HALO OF NGC 4649 (M60)

We apply the axisymmetric orbit superposition modeling to estimate the mass of the supermassive black hole and dark matter halo profile of NGC 4649. We have included data sets from the Hubble Space Telescope, stellar, and globular cluster observations. Our modeling gives the black hole mass = 4.5 \pm 1.0 10^9 \Msun and M/L = 8.7 \pm 1.0 (or 8.0 \pm 0.9 after foreground Galactic extinction is corrected). We confirm the presence of a dark matter halo, but the stellar mass dominates inside the effective radius. The parameters of the dark halo are less constrained due to the sparse globular cluster data at large radii. We find that in NGC 4649 the dynamical mass profile from our modeling is consistently larger than that derived from the X-ray data over most of the radial range by roughly 60% to 80%. It implies that either some forms of non-thermal pressure need to be included, the assumed hydrostatic equilibrium may not be a good approximation in the X-ray modelings of NGC 4649, or our assumptions used in the dynamical models are biased. Our new black hole mass is about two times larger than the previous published value; the earlier model did not adequately sample the orbits required to match the large tangential anisotropy in the galaxy center. If we assume that there is no dark matter, the results on the black hole mass and M/L do not change significantly, which we attribute to the inclusion of HST spectra, the sparse globular cluster kinematics, and a diffuse dark matter halo. Without the HST data, the significance of the black hole detection is greatly reduced.

Cascade events at IceCube + DeepCore as a definitive constraint on the dark matter interpretation of the PAMELA and Fermi anomalies

Dark matter decaying or annihilating into mu+mu- or tau+tau- has been proposed as an explanation for the e+e- anomalies reported by PAMELA and Fermi. Recent analyses show that IceCube, supplemented by DeepCore, will be able to significantly constrain the parameter space of decays to mu+mu-, and rule out decays to tau+tau- and annihilations to mu+mu- in less than five years of running. These analyses rely on measuring track-like events in IceCube+DeepCore from down-going nu_mu. In this paper we show that by instead measuring cascade events, which are induced by all neutrino flavors, IceCube+DeepCore can rule out decays to mu+mu- in only three years of running, and rule out decays to tau+tau- and annihilation to mu+mu- in only one year of running. These constraints are highly robust to the choice of dark matter halo profile and independent of dark matter-nucleon cross-section.

On the Sunyaev-Zel'dovich effect from dark matter annihilation or decay in galaxy clusters

We revisit the prospects for detecting the Sunyaev Zel'dovich (SZ) effect induced by dark matter (DM) annihilation or decay. We show that with standard (or even extreme) assumptions for DM properties, the optical depth associated with relativistic electrons injected from DM annihilation or decay is much smaller than that associated with thermal electrons, when averaged over the angular resolution of current and future experiments. For example, we find: τDM ∼ 10−9−10−5 (depending on the assumptions) for mχ = 1 GeV and a density profile ρ∝r−1 for a template cluster located at 50 Mpc and observed within an angular resolution of 10′′, compared to τth ∼ 10−3−10−2. This, together with a full spectral analysis, enables us to demonstrate that, for a template cluster with generic properties, the SZ effect due to DM annihilation or decay is far below the sensitivity of the Planck satellite. This is at variance with previous claims regarding heavier annihilating DM particles. Should DM be made of lighter particles, the current constraints from 511 keV observations on the annihilation cross section or decay rate still prevent a detectable SZ effect. Finally, we show that spatial diffusion sets a core of a few kpc in the electron distribution, even for very cuspy DM profiles, such that improving the angular resolution of the instrument, eg with ALMA, does not necessarily improve the detection potential. We provide useful analytical formulæ parameterized in terms of the DM mass, decay rate or annihilation cross section and DM halo features, that allow quick estimates of the SZ effect induced by any given candidate and any DM halo profile.

Determination of the local dark matter density in our Galaxy

The rotation curve, the total mass and the gravitational potential of the Galaxy are sensitive measurements of the dark matter halo profile. In this publication cuspy and cored DM halo profiles are analysed with respect to recent astronomical constraints in order to constrain the shape of the Galactic DM halo and the local DM density. All Galactic density components (luminous matter and DM) are parametrized. Then the total density distribution is constrained by astronomical observations: 1) the total mass of the Galaxy, 2) the total matter density at the position of the Sun, 3) the surface density of the visible matter, 4) the surface density of the total matter in the vicinity of the Sun, 5) the rotation speed of the Sun and 6) the shape of the velocity distribution within and above the Galactic disc. The mass model of the Galaxy is mainly constrained by the local matter density (Oort limit), the rotation speed of the Sun and the total mass of the Galaxy from tracer stars in the halo. It is shown from a statistical chi^2 fit to all data that the local DM density is strongly positively (negatively) correlated with the scale length of the DM halo (baryonic disc). Since these scale lengths are poorly constrained the local DM density can vary from 0.2 to 0.4 GeV/cm^3 (0.005 - 0.01 M_sun/pc^3) for a spherical DM halo profile and allowing total Galaxy masses up to 2 * 10^12 M_sun. For oblate DM halos and dark matter discs, as predicted in recent N-body simulations, the local DM density can be increased significantly.