Strong constraints on decay and annihilation of dark matter from heating of gas-rich dwarf galaxies

TL;DR

This study uses the ultra-low cooling rates of gas-rich dwarf galaxies to set new, strong constraints on dark matter decay and annihilation, especially for low-mass dark matter particles, surpassing previous limits.

Contribution

It provides model-independent bounds on dark matter decay and annihilation rates using gas-rich dwarf galaxies, improving constraints for low-mass dark matter and translating these bounds to various dark matter models.

Findings

Stronger bounds on DM decay lifetime for 1-10 MeV masses.

Competitive constraints on DM annihilation from CMB and gamma-ray surveys.

Potential of future surveys to probe diverse dark matter models.

Abstract

Gas-rich dwarf galaxies located outside the virial radius of their host are relatively pristine systems and have ultra-low gas cooling rates. This makes them very sensitive to heat injection by annihilation or decay of dark matter (DM). Such dwarfs are particularly sensitive to DM producing e$^\pm$ with energies 1$-$100 MeV or photons with energies 13.6 eV$-1$ keV, because these products can be efficiently thermalized in the neutral hydrogen gas of the dwarfs. Following the methodology of Wadekar and Farrar (2021), we require the rate of heat injection by DM to not exceed the ultra-low radiative cooling rate of gas in the Leo T dwarf galaxy. This gives model-independent bounds on $(i)$ the decay lifetime of DM to $e^\pm$ (photons) which are stronger than all the previous literature for $m_\mathrm{DM}\sim$ 1$-$10 MeV ($m_\mathrm{DM}\sim0.02-1$ keV), $(ii)$ annihilation of DM to $e^{\pm}$ comparable to constraints from CMB and X/$\gamma$-ray surveys. We also translate our bounds for the case of the following DM models: axion-like particles (ALPs), sterile neutrinos, excited DM states, higgs portal scalars and dark baryons. Observations of gas-rich low-mass dwarfs from upcoming 21cm and optical surveys can therefore be powerful probes of a multitude of models of DM.