Abstract
We search for an indirect signal of dark matter through very high-energy gamma rays from the Wolf-Lundmark-Melotte (WLM) dwarf irregular galaxy. The pair annihilation of dark matter particles would produce Standard Model particles in the final state such as gamma rays, which might be detected by ground-based Cherenkov telescopes. Dwarf irregular galaxies represent promising targets as they are dark matter dominated objects with well measured kinematics and small uncertainties on their dark matter distribution profiles. In 2018, the H.E.S.S. five-telescope array observed the dwarf irregular galaxy WLM for 18 hours. We present the first analysis based on data obtained from an imaging atmospheric Cherenkov telescope for this subclass of dwarf galaxy. As we do not observe any significant excess in the direction of WLM, we interpret the result in terms of constraints on the velocity-weighted cross section for dark matter pair annihilation as a function of the dark matter particle mass for various continuum channels as well as the prompt gamma-gamma emission. For the $\tau^+\tau^-$ channel the limits reach a $\langle \sigma v \rangle$ value of about $4\times 10^{-22}$ cm3s-1 for a dark matter particle mass of 1 TeV. For the prompt gamma-gamma channel, the upper limit reaches a $\langle \sigma v \rangle$ value of about $5 \times10^{-24}$ cm3s-1 for a mass of 370 GeV. These limits represent an improvement of up to a factor 200 with respect to previous results for the dwarf irregular galaxies for TeV dark matter search.
Highlights
Astrophysical observations suggest that nonbaryonic cold dark matter (DM) represents about 85% of the matter density in the Universe, affecting the formation of large scale structures, influencing the motion of galaxies and clusters, and bending the path of light
The telescopes detect brief flashes of Cherenkov radiation generated by very high energy γ rays
With its recent 18 hour observations of WLM, one of the most promising dwarf irregular galaxies, H.E.S.S. is the first imaging atmospheric Cherenkov telescope array to observe such a galaxy to search for DM annihilation signals
Summary
Astrophysical observations suggest that nonbaryonic cold dark matter (DM) represents about 85% of the matter density in the Universe, affecting the formation of large scale structures, influencing the motion of galaxies and clusters, and bending the path of light. They represent the smallest stellar systems with extended neutral hydrogen (HI) distributions [7] This large amount of gas is detectable by radio telescopes and is used as a kinematic tracer for deriving the rotation curves up to large radii of the galaxies [8]. This new search complements the studies carried out for DM from dwarf spheroidal galaxies [10,11,12] and from the galactic center [13,14].
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