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Register a new userDark matter annihilation and decay profiles for the Reticulum II dwarf spheroidal galaxy
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The dwarf spheroidal galaxies (dSph) of the Milky Way are among the most attractive targets for indirect searches of dark matter. In this work, we reconstruct the dark matter annihilation (J-factor) and decay profiles for the newly discovered dSph Reticulum II. Using an optimized spherical Jeans analysis of kinematic data obtained from the Michigan/Magellan Fiber System (M2FS), we find Reticulum IIs J-factor to be among the largest of any Milky Way dSph. We have checked the robustness of this result against several ingredients of the analysis. Unless it suffers from tidal disruption or significant inflation of its velocity dispersion from binary stars, Reticulum II may provide a unique window on dark matter particle properties.
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Andrew B. Pace George P. andn Cynthia Woods Mitchell Institute for Fundamental Physics
, Astronomy
2018
Measuring the dark matter distribution in dwarf spheroidal galaxies (dSphs) from stellar kinematics is crucial for indirect dark matter searches, as these distributions set the fluxes for both dark matter annihilation (J-Factor) and decay (D-Factor). Here we produce a compilation of J and D-Factors for dSphs, including new calculations for several newly-discovered Milky Way (MW) satellites, for dSphs outside of the MW virial radius, and for M31 satellites. From this compilation we test for scaling relations between the J and D-factors and physical properties of the dSphs such as the velocity dispersion ($sigma_{mathrm{los}}$), the distance ($d$), and the stellar half-light radius ($r_{1/2}$). We find that the following scaling relation minimizes the residuals as compared to different functional dependencies on the observed dSphs properties $J(0.5 {rm deg}) = 10^{17.72} left(sigma_{mathrm{los}}/5,{rm km , s^{-1}}right)^4 left(d / 100,{rm kpc}right)^{-2}left( r_{1/2}/100 ,{rm pc} right)^{-1}$. We find this relation has considerably smaller scatter as compared to the simpler relations that scale only as $1/d^2$. We further explore scalings with luminosity ($L_V$), and find that the data do not strongly prefer a scaling including $L_V$ as compared to a pure $1/d^2$ scaling. The scaling relations we derive can be used to estimate the J-Factor without the full dynamical analysis, and will be useful for estimating limits on particle dark matter properties from new systems that do not have high-quality stellar kinematics.
Dwarf spheroidal (dSph) galaxies are prime targets for present and future gamma-ray telescopes hunting for indirect signals of particle dark matter. The interpretation of the data requires careful assessment of their dark matter content in order to derive robust constraints on candidate relic particles. Here, we use an optimised spherical Jeans analysis to reconstruct the `astrophysical factor for both annihilating and decaying dark matter in 21 known dSphs. Improvements with respect to previous works are: (i) the use of more flexible luminosity and anisotropy profiles to minimise biases, (ii) the use of weak priors tailored on extensive sets of contamination-free mock data to improve the confidence intervals, (iii) systematic cross-checks of binned and unbinned analyses on mock and real data, and (iv) the use of mock data including stellar contamination to test the impact on reconstructed signals. Our analysis provides updated values for the dark matter content of 8 `classical and 13 `ultrafaint dSphs, with the quoted uncertainties directly linked to the sample size; the more flexible parametrisation we use results in changes compared to previous calculations. This translates into our ranking of potentially-brightest and most robust targets---viz., Ursa Minor, Draco, Sculptor---, and of the more promising, but uncertain targets---viz., Ursa Major 2, Coma---for annihilating dark matter. Our analysis of Segue 1 is extremely sensitive to whether we include or exclude a few marginal member stars, making this target one of the most uncertain. Our analysis illustrates challenges that will need to be addressed when inferring the dark matter content of new `ultrafaint satellites that are beginning to be discovered in southern sky surveys.
We present the first observational limits on the predicted synchrotron signals from particle Dark Matter annihilation models in dwarf spheroidal galaxies at radio frequencies below 1 GHz. We use a combination of survey data from the Murchison Widefield Array (MWA) and the Giant Metre-wave Radio Telescope (GMRT) to search for diffuse radio emission from 14 dwarf spheroidal galaxies. For in-situ magnetic fields of 1 $mu G$ and any plausible value for the diffusion coefficient, our limits do not constrain any Dark Matter models. However, for stronger magnetic fields our data might provide constraints comparable to existing limits from gamma-ray and cosmic ray observations. Predictions for the sensitivity of the upgraded MWA show that models with Dark Matter particle mass up to $sim$ 1.6 TeV (1 TeV) may be constrained for magnetic field of 2 $mu G$ (1 $mu G$). While much deeper limits from the future low frequency Square Kilometre Array (SKA) will challenge the LHC in searches for Dark Matter particles, the MWA provides a valuable first step toward the SKA at low frequencies.
We search for an indirect signal of dark matter through very high-energy gamma rays from the Wolf-Lundmark-Melotte (WLM) dwarf irregular galaxy. The pair annihilation of dark matter particles would produce Standard Model particles in the final state such as gamma rays, which might be detected by ground-based Cherenkov telescopes. Dwarf irregular galaxies represent promising targets as they are dark matter dominated objects with well measured kinematics and small uncertainties on their dark matter distribution profiles. In 2018, the H.E.S.S. five-telescope array observed the dwarf irregular galaxy WLM for 18 hours. We present the first analysis based on data obtained from an imaging atmospheric Cherenkov telescope for this subclass of dwarf galaxy. As we do not observe any significant excess in the direction of WLM, we interpret the result in terms of constraints on the velocity-weighted cross section for dark matter pair annihilation as a function of the dark matter particle mass for various continuum channels as well as the prompt gamma-gamma emission. For the $tau^+tau^-$ channel the limits reach a $langle sigma v rangle$ value of about $4times 10^{-22}$ cm3s-1 for a dark matter particle mass of 1 TeV. For the prompt gamma-gamma channel, the upper limit reaches a $langle sigma v rangle$ value of about $5 times10^{-24}$ cm3s-1 for a mass of 370 GeV. These limits represent an improvement of up to a factor 200 with respect to previous results for the dwarf irregular galaxies for TeV dark matter search.
Dwarf spheroidal galaxies of the Local Group are close satellites of the Milky Way characterized by a large mass-to-light ratio and are not expected to be the site of non-thermal high-energy gamma-ray emission or intense star formation. Therefore they are amongst the most promising candidates for indirect dark matter searches. During the last years the High Energy Stereoscopic System (H.E.S.S.) of imaging atmospheric Cherenkov telescopes observed five of these dwarf galaxies for more than 140 hours in total, searching for TeV gamma-ray emission from annihilation of dark matter particles. The new results of the deep exposure of the Sagittarius dwarf spheroidal galaxy, the first observations of the Coma Berenices and Fornax dwarves and the re-analysis of two more dwarf spheroidal galaxies already published by the H.E.S.S. Collaboration, Carina and Sculptor, are presented. In the absence of a significant signal new constraints on the annihilation cross-section applicable to Weakly Interacting Massive Particles (WIMPs) are derived by combining the observations of the five dwarf galaxies. The combined exclusion limit depends on the WIMP mass and the best constraint is reached at 1-2 TeV masses with a cross-section upper bound of ~3.9x10-24 cm^3 s-1 at a 95% confidence level.
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