Search for Gamma-Ray Emission from DES Dwarf Spheroidal Galaxy Candidates with Fermi-LAT Data

TLDR: In this article, the authors search for gamma-ray emission coincident with the positions of these new objects in six years of Fermi Large Area Telescope data and find no significant excesses of gamma radiation emission.

Abstract: Due to their proximity, high dark-matter (DM) content, and apparent absence of non-thermal processes, Milky Way dwarf spheroidal satellite galaxies (dSphs) are excellent targets for the indirect detection of DM. Recently, eight new dSph candidates were discovered using the first year of data from the Dark Energy Survey (DES). We searched for gamma-ray emission coincident with the positions of these new objects in six years of Fermi Large Area Telescope data. We found no significant excesses of gamma-ray emission. Under the assumption that the DES candidates are dSphs with DM halo properties similar to the known dSphs, we computed individual and combined limits on the velocity-averaged DM annihilation cross section for these new targets. If the estimated DM content of these dSph candidates is confirmed, they will constrain the annihilation cross section to lie below the thermal relic cross section for DM particles with masses ≲ 20 {GeV} annihilating via the b\bar{b} or tau+tau- channels.

Figures

Figure 3. J-factor distance scaling. Black points are from Table 1 in Ackermann et al. (2014). The red curve is our best fit with an assumed inverse square distance relation (see the text). The red band shows the 0.4 dex uncertainty that we adopt.

Table 1 DES dSph Candidates and Estimated J-factors

Figure 4. Upper limits on the velocity-averaged DM annihilation cross section at 95% confidence level for DM annihilation to bb̄(left) and τ+τ−(right) derived using distance-estimated J-factors. Individual limits for each DES candidate dSph, as well as the combined limits (dashed red line) from the eight new candidates are shown. Here we assume that each candidate is a dSph and that future kinematic analyses will confirm the J-factors estimated based on photometric data (see the text). For reference, we show the current best limits derived from a joint analysis of 15 previously known dSphs with kinematically constrained J-factors (black curve) (Ackermann et al. 2015a). The dashed gray curve shows the thermal relic cross section derived by Steigman et al. (2012).

Figure 1. LAT counts maps in10 10 ´ ROI centered at each DES dSph candidate (white “×” symbols), for E 1 GeV> , smoothed with a 0. 25 Gaussian kernel. All 3FGL sources in the ROI are indicated with white “+” symbols, and those with TS 100> are explicitly labeled.

Figure 2. Bin-by-bin integrated energy-flux upper limits at 95% confidence level for the eight DES dSph candidates modeled as point-like sources.