Dwarf Galaxy Reticulum II's MeerKAT L-Band Observation: Constraining WIMP Dark Matter

Abstract

The nature of dark matter remains one of the most profound open questions in modern physics, with weakly interacting massive particles (WIMPs) among the leading candidates proposed to account for the observed anomalies across cosmic scales. If WIMPs annihilate or decay in the dense dark matter haloes of nearby galaxies, the resulting high-energy electrons/positrons can produce synchrotron radiation in the presence of ambient magnetic fields, yielding a potentially detectable radio signature. Dwarf spheroidal galaxies are particularly promising targets for indirect dark matter searches due to their high mass-to-light ratios and low astrophysical foreground contamination. While radio observations have been widely used to constrain WIMP properties in these systems, the resulting limits remain highly sensitive to poorly constrained magnetic field assumptions. Here we utilize L-band ($1.3$--$1.5$ GHz) observations from the MeerKAT array directed towards dwarf galaxy Reticulum II and measure the surface brightness profile across the dwarf galaxy. Combining these measurements with theoretical models of WIMP annihilation and yield 95% confidence level upper limits on the WIMP annihilation cross-section $\langleσv\rangle \lesssim 10^{-26}$ cm$^3$ s$^{-1}$ for masses $m_χ\sim 10$-$200$ GeV (with the assumed uniform magnetic field model and diffusion constant). As next-generation radio facilities such as the Square Kilometre Array come online, robust characterisation of magnetic environments in dwarf galaxies will be essential to fully exploit their sensitivity to the particle nature of dark matter.