Search for gamma-ray emission from eight dwarf spheroidal galaxy candidates discovered in year two of Dark Energy Survey with Fermi-LAT data

Abstract

Very recently the Dark Energy Survey (DES) Collaboration has released their second group of Dwarf spheroidal (dSph) galaxy candidates. With the publicly-available Pass 8 data of Fermi-LAT we search for γ−ray emissions from the directions of these eight newly discovered dSph galaxy candidates. No statistically significant γ−ray signal has been found in the combined analysis of these sources. With the empirically estimated J-factors of these sources, the constraint on the annihilation channel of χχ → τ + τ − is comparable to the bound set by the joint analysis of fifteen previously known dSphs with kinematically constrained J-factors for the dark matter mass m χ > 250 GeV. In the direction of Tucana III (DES J2356-5935), one of the nearest dSph galaxy candidates that is ∼ 25 kpc away, there is a weak γ−ray signal and its peak test statistic (TS) value for the dark matter annihilation channel χχ → τ + τ −1 is ≈ 6.7 at m χ ∼ 15 GeV. The significance of the possible signal likely increases with time. More data is highly needed to pin down the physical origin of such a GeV excess. PACS numbers: 95.35.+d, 95.85.Pw, 98.52.Wz

Searching for Dark Matter Annihilation in Recently Discovered Milky Way Satellites With Fermi-Lat

“…After the completion of this analysis, we became aware of an independent study of LAT Pass 8 data coincident with DES Y2 dSph candidates (Li et al 2016). The γ-ray results associated with individual targets are consistent between the two works; however, the samples selected for combined analysis are different.…”

“…Many groups have searched for excess γ rays associated with dSphs using LAT data and have reported constraints on DM annihilation that are competitive with other DM targets such as the Galactic center (e.g., Abdo et al 2010;Ackermann et al 2011;Geringer-Sameth & Koushiappas 2011;Mazziotta et al 2012;Geringer-Sameth et al 2015b, 2015cLi et al 2016). For example, the combined likelihood analysis of 15 dSphs with six years of LAT Pass 8 data by Ackermann et al (2015b) excludes DM particles with masses 100 GeV annihilating with the canonical thermal relic cross section via quark or τ-lepton channels.…”

Sommerfeld-enhanced J -factors for dwarf spheroidal galaxies

“…Within the context of our spherically-symmetric and isotropic model for the dark matter phase space distribution, we quantify the astrophysical uncertainty in the J S -factors and show that the relative ordering of the most promising J S -factors can be interchanged relative to the standard velocity-independent J-factors. This result may have important implications for the interpretation of possible gamma-ray excesses from a dSph [37,38].…”

Probing dark matter annihilation in the Galaxy with antiprotons and gamma rays

“…Four of these dwarfs (Reticulum II, Tucana III, Tucana IV, Indus II) exhibit small excesses at the level of ∼ 2σ (local) each, which are compatible with a signal from DM annihilation with a thermal cross section [58,60,61]. The total likelihood is obtained as a product of likelihoods over each single dwarf as described in [57,62].…”