Glow in the Dark Matter: Observing galactic halos with scattered light

TL;DR

This paper proposes using the diffuse light halos around spiral galaxies to constrain dark matter-photon interactions, demonstrating that current observations can set upper limits and that multi-wavelength data can enhance detection prospects.

Contribution

It introduces a novel observational method using galactic halos to probe dark matter-photon scattering, providing new constraints and potential for discovery.

Findings

Dark matter halos can scatter light, affecting surface brightness profiles.

Current data from the Dragonfly instrument set upper limits on DM-photon cross section.

Multi-wavelength observations can improve constraints and aid detection.

Abstract

We consider the observation of diffuse halos of light around the discs of spiral galaxies, as a probe of the interaction cross section between Dark Matter and photons. Using the galaxy M101 as an example, we show that for a scattering cross section at the level of 10^(-23) x (m/GeV) cm^2 or greater Dark Matter in the halo will scatter light out from the more luminous centre of the disc to larger radii, contributing to an effective increased surface brightness at the edges of the observed area on the sky. This allows us to set an upper limit on the DM-photon cross section using data from the Dragonfly instrument. We then show how to improve this constraint, and the potential for discovery, by combining the radial profile of DM-photon scattering with measurements at multiple wavelengths. Observation of diffuse light presents a new and potentially powerful way to probe the interactions of Dark Matter with photons, which is complimentary to existing searches.