H.E.S.S. observations of the globular clusters NGC 6388 and M 15 and search for a Dark Matter signal

TL;DR

This study used H.E.S.S. telescopes to observe globular clusters NGC 6388 and M 15, searching for dark matter signals, but found no gamma-ray emissions and set limits on dark matter annihilation cross sections.

Contribution

First to model dark matter content in globular clusters considering astrophysical effects and derive constraints on dark matter annihilation cross sections from gamma-ray observations.

Findings

No gamma-ray signals detected from NGC 6388 and M 15.

Set 95% confidence level limits on dark matter annihilation cross sections.

Limits in the TeV range are at 10-25 and a few 10-24 cm³/s for NGC 6388 and M 15.

Abstract

Observations of the globular clusters NGC 6388 and M 15 were carried out by the H.E.S.S. array of Cherenkov telescopes for a live time of 27.2 and 15.2 hours respectively. No gamma-ray signal is found at the nominal target position of NGC 6388 and M 15. In the primordial formation scenario, globular clusters are formed in a dark matter halo and dark matter could still be present in the baryon-dominated environment of globular clusters. This opens the possibility of observing a dark matter self-annihilation signal. The dark matter content of the globular clusters NGC 6388 and M 15 is modelled taking into account the astrophysical processes that can be expected to influence the dark matter distribution during the evolution of the globular cluster: the adiabatic contraction of dark matter by baryons, the adiabatic growth of a black hole in the dark matter halo and the kinetic heating of dark matter by stars. 95% confidence level exclusion limits on the dark matter particle velocity-weighted annihilation cross section are derived for these dark matter haloes. In the TeV range, the limits on the velocity-weighted annihilation cross section are derived at the 10-25 cm3 s-1 level and a few 10-24 cm3 s-1 for NGC 6388 and M 15 respectively.