Dark matter annihilation and decay in dwarf spheroidal galaxies: the classical and ultrafaint dSphs

Abstract

Dwarf spheroidal (dSph) galaxies are prime targets for present and future γ-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 crosschecks 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.

Foreground effect on the J-factor estimation of classical dwarf spheroidal galaxies

“…The results give 60 − 100 % deviation for the J-factors from the spherical estimation. A consistent result is also derived by Bonnivard et al (2015b), where they estimate the effect of the non-sphericity using mock stellar samples.…”

“…Because the anisotropy parameter cannot be directly addressed, one should make assumptions on the spatial dependence of the anisotropy. Currently, most studies assume that the anisotropy is r-independent, while the recent study (Bonnivard et al 2015b) fits the kinematical data by using the Baes & van Hase parametrization (Baes & Van Hese 2007). Since it is pointed out that the anisotropy parameter might give a non-negligible effect on the J-factor estimation (Ullio & Valli 5 Another approach is to impose the empirical parameter cut (Bonnivard et al 2015b).…”

“…As pointed out in Bhattacherjee et al (2014), however, the constraints crucially depend on the astrophysical uncertainties of the dark halo shape of the dSphs especially the ones of the so-called ultra-faint dSphs whose numbers of the observed stars are less than O(100). Recent detailed analyses have also revealed hidden but non-negligible uncertainties of the dark matter profile: prior bias (Martinez et al 2009), anisotropy of the velocity dispersion (Ullio & Valli 2016), size of the halo truncation (Geringer-Sameth et al 2015), non-sphericity (Bonnivard et al 2015b;Hayashi et al 2016), and foreground contamination (Bonnivard et al 2016). 2 These systematic uncertainties are partly caused by the lack of sufficiently large stellar kinematic data available from current spectroscopic instruments.…”

Sommerfeld-enhanced J -factors for dwarf spheroidal galaxies

“…With this assumption the J-factor is independent of the underlying particle physics such as the dark matter mass and cross section, and furthermore, it is independent of the particular phase space distribution of the dark matter. Many authors have determined the J-factors from the stellar kinematics of dSphs under the assumption of a velocity-independent annihilation cross section [10][11][12][13][14][15].…”

Search for Dark Matter Annihilations towards the Inner Galactic Halo from 10 Years of Observations with H.E.S.S.

“…[24] could be overestimated by a factor of 100 as shown in Ref. [26]), the combined analysis of four dwarf galaxies observed by H.E.S.S. [25], and the observations of 15 dwarf galaxy satellites of the Milky Way by the Fermi satellite [23].…”