107 research outputs found

    γ\gamma-ray flux from Dark Matter Annihilation in Galactic Caustics

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    In the frame of indirect dark matter searches we investigate the flux of high-energy γ\gamma-ray photons produced by annihilation of dark matter in caustics within our Galaxy under the hypothesis that the bulk of dark matter is composed of the lightest supersymmetric particles. Unfortunately, the detection of the caustics annihilation signal with currently available instruments is rather challenging. Indeed, with realistic assumptions concerning particle physics and cosmology, the γ\gamma -ray signal from caustics is below the detection threshold of both Cˇ\check {\rm C}erenkov telescopes and satellite-borne experiments. Nevertheless, we find that this signal is more prominent than that expected if annihilation only occurs in the smoothed Galactic halo, with the possible exception of a ∼15∘\sim 15^{\circ} circle around the Galactic center if the mass density profile of our Galaxy exhibits a sharp cusp there. We show that the angular distribution of this γ\gamma-ray flux changes significantly if DM annihilation preferentially occurs within virialized sub-halos populating our Galaxy rather than in caustics.Comment: 17 pages, 8 figures. Accepted for publication in JCA

    On the detectability of gamma-rays from Dark Matter annihilation in the Local Group with ground-based experiments

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    Recent studies have suggested the possibility that the lightest supersymmetric particle is a suitable dark matter candidate. In this theoretical framework, annihilations in high density environments like the center of dark matter haloes may produce an intense flux of gamma-rays. In this paper we discuss the possibility of detecting the signatures of neutralino annihilation in nearby galaxies with next generation ground-based detectors.Comment: to appear in Proceedings of ICRC 200

    On the recovery of Local Group motion from galaxy redshift surveys

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    There is a ∼150kms−1\sim 150 km s^{-1} discrepancy between the measured motion of the Local Group of galaxies (LG) with respect to the CMB and the linear theory prediction based on the gravitational force field of the large scale structure in full-sky redshift surveys. We perform a variety of tests which show that the LG motion cannot be recovered to better than 150−200kms−1150-200 km s^{-1} in amplitude and within a ≈10∘\approx10^\circ in direction. The tests rely on catalogs of mock galaxies identified in the Millennium simulation using semi-analytic galaxy formation models. We compare these results to the Ks=11.75K_s=11.75 Two-Mass Galaxy Redshift Survey, which provides the deepest, widest and most complete spatial distribution of galaxies available so far. In our analysis we use a new, concise relation for deriving the LG motion and bulk flow from the true distribution of galaxies in redshift space. Our results show that the main source of uncertainty is the small effective depth of surveys like the 2MRS that prevents a proper sampling of the large scale structure beyond ∼100h−1Mpc\sim100 h^{-1} Mpc. Deeper redshift surveys are needed to reach the "convergence scale" of ≈250h−1Mpc\approx 250 h^{-1}Mpc in a Λ\LambdaCDM universe. Deeper survey would also mitigate the impact of the "Kaiser rocket" which, in a survey like 2MRS, remains a significant source of uncertainty. Thanks to the quiet and moderate density environment of the LG, purely dynamical uncertainties of the linear predictions are subdominant at the level of ∼90kms−1\sim 90 km s^{-1}. Finally, we show that deviations from linear galaxy biasing and shot noise errors provide a minor contribution to the total error budget.Comment: 14 pages, 7 figure

    Growth rate of cosmological perturbations at z ~ 0.1 from a new observational test

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    Spatial variations in the distribution of galaxy luminosities, estimated from redshifts as distance proxies, are correlated with the peculiar velocity field. Comparing these variations with the peculiar velocities inferred from galaxy redshift surveys is a powerful test of gravity and dark energy theories on cosmological scales. Using ~ 2 ×\times 105^{5} galaxies from the SDSS Data Release 7, we perform this test in the framework of gravitational instability to estimate the normalized growth rate of density perturbations fσ8\sigma_{8} = 0.37 +/- 0.13 at z ~ 0.1, which is in agreement with the Λ\LambdaCDM scenario. This unique measurement is complementary to those obtained with more traditional methods, including clustering analysis. The estimated accuracy at z ~ 0.1 is competitive with other methods when applied to similar datasets.Comment: 4 pages, 2 figures, matches version accepted for publication in PR

    Dark Matter Annihilation in Substructures Revised

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    Upcoming γ\gamma-ray satellites will search for Dark Matter annihilations in Milky Way substructures (or 'clumps'). The prospects for detecting these objects strongly depend on the assumptions made on the distribution of Dark Matter in substructures, and on the distribution of substructures in the Milky Way halo. By adopting simplified, yet rather extreme, prescriptions for these quantities, we compute the number of sources that can be detected with upcoming experiments such as GLAST, and show that, for the most optimistic particle physics setup (mχ=40m_\chi=40 GeV and annihilation cross section σv=3×10−26\sigma v = 3 \times 10^{-26} cm3^3 s−1^{-1}), the result ranges from zero to ∼\sim hundred sources, all with mass above 105M⊙10^{5}M\odot. However, for a fiducial DM candidate with mass mχ=100m_\chi=100 GeV and σv=10−26\sigma v = 10^{-26} cm3^3 s−1^{-1}, at most a handful of large mass substructures can be detected at 5σ5 \sigma, with a 1-year exposure time, by a GLAST-like experiment. Scenarios where micro-clumps (i.e. clumps with mass as small as 10−6M⊙10^{-6}M\odot) can be detected are severely constrained by the diffuse γ\gamma-ray background detected by EGRET.Comment: Version accepted for publication in MNRAS. Other subhalos mass function slopes added. All-sky analysis performed. Boost factors added. High resolution figures for all models in http://www2.iap.fr/users/bertone/Clumps

    Modelling the Power Spectrum of Density Fluctuations: A Phenomenological Approach

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    We show how, based on considerations on the observed form of the galaxy 2-point spatial correlation function xi(r), a very simplified -- yet surprisingly effective -- model for the linear density fluctuations power spectrum can be constructed. We first relate the observed large-scale shape of xi(r) to a power-law form for the power spectrum, P(k)\propto k^{-2.2}. For a plausible value of the bias parameter b = 1/sigma_8 ~ 1.8, one has (delta_rho / rho)_{rms} ~ 1 r ~ 3.5/h Mpc, suggesting that the change of slope observed in xi(r) around this scale marks the transition between the linear and nonlinear gravitational regimes. Under this working hypothesis, we use a simple analytical form to fit the large-scale correlations constraints together with the COBE CMB anisotropy measurement, thus constructing a simple phenomenological model for the linear power spectrum. Despite its simplicity, the model fits remarkably well directly estimated power spectra from different optical galaxy samples, and when evolved through an N-body simulation it provides a good match to the observed galaxy correlations. One of the most interesting features of the model is the small-scale one-dimensional velocity dispersion produced: sigma_{1d} = 450 Km s^{-1} at 0.5/h Mpc and sigma_{1d} = 350 Km s^{-1} for separations larger than ~ 2/h Mpc.Comment: ApJL in press, 10 pages in plain TeX, 3 figures available from [email protected], SISSA 110/93/
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