Galactic Center Gamma-Ray Excess from a Generic Triaxial Halo

TL;DR

This study investigates how the shape and orientation of a triaxial dark matter halo influence the Galactic Center Excess observed in gamma-ray data, finding that morphology can distinguish dark matter from stellar origins.

Contribution

It provides the first detailed analysis of the GCE's morphology considering a triaxial and tilted dark matter halo, enhancing understanding of its potential dark matter origin.

Findings

GCE spectrum and cuspiness are robust against halo shape variations.

GCE morphology can differentiate between dark matter and stellar sources.

Triaxial and tilted dark matter halos better explain the GCE than stellar halos.

Abstract

Recent studies of Galactic surveys, such as Gaia, have revealed that the Milky Way's gravitational potential comes from a matter distribution that is triaxial and rotated with respect to the Galactic center-Sun axis. This, in turn, could mean that the dark matter halo also shares these properties. In this work, by fitting to the Fermi-LAT gamma-ray observations, we test the compatibility of the morphology of the Galactic Center Excess (GCE) from dark matter annihilation with a triaxial dark matter halo. In particular, we consider both untilted triaxial halos and halos whose principal axes are tilted with respect to the Galactic disk. In our fits of the Fermi-LAT data, by testing over a large library of galactic diffuse emission models, we quantify how the halo triaxiality and tilt affect the line-of-sight-integrated annihilation signal and, consequently, the preferred GCE spatial templates. We find that the GCE spectrum and inner cuspiness are robust against variations in the triaxiality and tilt of the dark matter halo. However, in terms of its overall morphology, the GCE in the gamma-ray data can discriminate between choices for the dark matter halo's triaxiality and tilt. Finally, we find that the GCE is more compatible with originating from a triaxial and tilted halo of dark matter than originating from a triaxial and tilted halo of stars, a result important for understanding the GCE's origin.