The 111 and 129 GeV gamma-ray lines from annihilations in the Milky Way dark matter halo, dark disk and subhalos

TL;DR

This paper investigates the 110-130 GeV gamma-ray lines observed in the Milky Way, analyzing their potential origin from dark matter annihilations in the halo, substructures, and galaxy clusters, and explores the morphology and distribution of these signals.

Contribution

It provides a comprehensive analysis of gamma-ray line signals, comparing observations with simulations, and assesses the role of dark matter substructures, disks, and background models in explaining the signals.

Findings

Extrapolations of substructure models can account for point source signals.

A spherical, cuspier dark matter halo profile is preferred.

Thin dark disks are not disfavored and could explain the distribution of signals.

Abstract

Recently a series of indications have been put forward suggesting the presence of two gamma-ray lines at 110-130 GeV (centered at 111 and 129 GeV). Signals of these lines have been observed toward the Galactic center, at some galaxy clusters and among some of the unassociated point sources of the 2 years Fermi catalogue. Such a combination of signals could be generated by dark matter annihilations in the main dark matter halo, its substructures and nearby galaxy clusters. We discuss in this work the consistency between the number of events observed at the line energies in the sky and the predictions using results from the Via Lactea II numerical simulation and extrapolations below its mass resolution, taking into account that the annihilation cross-section to the lines can be estimated from the Galactic center signal. We find that some extrapolations to small substructures can naturally account for the point sources signal, although the hypothesis of background only cannot be rejected. We also study the morphology of the gamma-ray sky at the 2 lines energies, testing different Galactic diffuse background models to account for interstellar medium uncertainties, and different assumptions on the DM diffuse component profile. We find from template fits that within reasonable diffuse background uncertainties the presence of a spherical halo component is preferred with cuspier dark matter halo profiles being preferable even from the full sky fit. We finally check the impact of a dark disk component, suggested by cosmological simulations that include baryons and find that thin dark disks can not be disfavored, thus possibly accounting for the preferentially closer to the Galactic disk distribution of the point sources lines signal.