Could the Fermi Large Area Telescope detect γ-rays from dark matter annihilation in the dwarf galaxies of the Local Group?

Abstract

Context. The detection of γ-rays from dark matter (DM) annihilation is among the scientific goals of the Fermi Large Area Telescope (formerly known as GLAST) and Cherenkov telescopes. Aims. In this paper we investigate the chances of such a discovery, selecting some nearby dwarf spheroidal galaxies (dSph) as a target, and adopting the DM density profiles derived from both astronomical observations and N-body simulations. We also make use of recent studies about the presence of black holes and of a population of sub-subhalos inside the Local Group (LG) dwarfs to carry out boost factor studies. Methods. We study the detectability with the Fermi-LAT of the γ-ray flux from DM annihilation in four of the nearest and highly DM-dominated dSph galaxies of the LG, namely Draco, Ursa Minor, Carina, and Sextans, for which state-of-art DM density profiles were available. We assume the DM is made of weakly interacting massive particles such as the lightest supersymmetric particle and compute the expected γ-ray flux for estimations of the unknown underlying particle physics parameters. We then compute the boost factors due to the presence of DM clumps and of a central supermassive black hole. Finally, we compare our predictions with the Fermi-LAT sensitivity maps. Results. We find that the dSph galaxies shine above the Galactic smooth halo: e.g., the Galactic halo is brighter than the Draco dSph only for angles smaller than 2.3 degrees above the Galactic Center. We also find that the presence of a cusp or a constant density core in the DM mass density profile does not produce any relevant effects in the γ-ray flux due to the fortunate combination of the geometrical acceptance of the Fermi-LAT detector and the distance of the galaxies. Moreover, no significant enhancement is given by the presence of a central black hole or a population of sub-subhalos. Conclusions. We conclude that, even for the most optimistic scenario of particle physics, the γ-ray flux from DM annihilation in the dSph galaxies of the LG would be too low to be detected with the Fermi-LAT.

Characterization of subhalo structural properties and implications for dark matter annihilation signals

“…Several analytical approaches based on the extended Press-Schechter theory have addressed the properties of the subhalo population in larger halos (see, e.g., Pieri et al (2008); Giocoli et al (008a, 2009);Pieri et al (2009)) and used results from early N-body cosmological simulations about the distribution of subhalos in host halos (Diemand et al 005b,a) to estimate the impact on gamma-ray searches. Also, more refined simulations in the past years have allowed us to better characterize the population and the structure of DM subhalos (Kuhlen et al 2008;Springel et al 2008;Diemand et al 2008;Hellwing et al 2015;Rodríguez-Puebla et al 2016) and different algorithms have been proposed in order to identify small structures within simulated host halos (Ghigna et al 2000;Weller et al 2005;Shaw et al 2006;Springel et al 2001;Gill et al 004a,b;Tormen & Moscardini 2004;Giocoli et al 008b, 2010;Han et al 2012;Behroozi et al 2013).…”

Substructure boosts to dark matter annihilation from Sommerfeld enhancement

“…That dSphs make good candidates for DM annihilation detection has been much discussed before, especially for the "classical", or pre-SDSS, dSphs [62,110,142,143,144,145]. The annihilation signal coming from Draco has been the subject of much research in recent years because of its relative proximity to the Earth [65,110,144,146,147,148,149,150]. The prospects for DM annihilation detection from dSphs has in general been found to be rather poor, with detection with Fermi being unlikely [150,151].…”

“…The annihilation signal coming from Draco has been the subject of much research in recent years because of its relative proximity to the Earth [65,110,144,146,147,148,149,150]. The prospects for DM annihilation detection from dSphs has in general been found to be rather poor, with detection with Fermi being unlikely [150,151]. Some of the dSphs have already been the subject of observational searches for DM annihilation and some limits on the DM annihilation signal have already been set [152,153,154,155,156,157].…”

Complementarity of indirect and accelerator dark matter searches

“…The most promising targets are the Galactic center (GC) [18][19][20][21][22][23] and substructures in the Milky Way halo, including dwarf galaxies [24][25][26][27][28][29][30][31] and intermediate-mass black holes [32][33][34][35][36][37][38][39].…”