Searching for light in the darkness: Bounds on ALP dark matter with the optical MUSE-faint survey

Marco Regis,Marco Taoso,Daniel Vaz,Jarle Brinchmann,Sebastiaan L Zoutendijk,Nicolas F Bouché,Matthias Steinmetz

doi:10.1016/j.physletb.2021.136075

Abstract

We use MUSE spectroscopic observations of the dwarf spheroidal galaxy Leo T between 470 and 935 nm to search for radiative decays of axion like particles (ALPs). Under the assumption that ALPs constitute the dark matter component of the Leo T halo, we derive bounds on the effective ALP-two-photon coupling. We improve existing limits by more than one order of magnitude in the ALP mass range 2.7-5.3 eV.

Highlights

Axion-like particles (ALPs) are compelling cold dark matter candidates [1, 2, 3]
The central region of Leo T was observed as part of Multi Unit Spectroscopic Explorer (MUSE)-Faint [30], a Guaranteed Time Observing (GTO) survey of ultra-faint dwarf galaxies (PI Brinchmann) with MUSEww, a large-field medium-resolution Integral Field Spectrograph on the Very Large Telescope (VLT)
The limit on gaγγ becomes more stringent as the mass ma increases. This is due to the scaling of the decay rate as Γa ∝ m3a. Another estimate of the D-factor can be obtained using the results of ref. [42], considered in ref. [43], which exploits 21 cm radio observations to infer the dark matter distribution of Leo T, described with NFW and Burkert profiles

Summary

Introduction

Axion-like particles (ALPs) are compelling cold dark matter candidates [1, 2, 3]. They are a generalization of the QCD axion, which was originally introduced to solve the strong charge-parity (CP) problem [4, 5, 6, 7]. For ALP masses in the eV range, the monochromatic line emission from ALP decays falls in the optical and near infrared bands Upper limits on this signal have been obtained from observations of galaxy clusters in Ref. This anomaly can be interpreted in terms of ALPs with masses < 100 eV produced in the interior of the Sun and detected by the Xenon1T experiment through the axioelectric effect, exploiting the couplings of ALPs with electrons 3 While this result calls for further examination, it certainly spurs interest in ALPs. Dwarf spheroidal galaxies are ideal targets to search for indirect dark matter signals, given their proximity and their high dark matter content.

Observations and data reduction

ALP signal

NpFixW HM

Conclusions