Cosmic-ray transport and gamma-ray emission in M31

TL;DR

This study explores how cosmic-ray electrons and protons, possibly originating from various sources and diffusion scenarios, could explain the extensive gamma-ray emission observed in the Andromeda Galaxy, M31.

Contribution

It introduces a comprehensive analysis of cosmic-ray transport models and evaluates their role in producing M31's gamma-ray emission, including effects of diffusion inefficiencies and pulsar contributions.

Findings

Cosmic-ray particles can account for gamma-ray emission up to 100 kpc from M31's center.

Diffusion scenarios with regions of inefficient diffusion are consistent with observed gamma-ray profiles.

Pulsar emissions may also contribute to the gamma-ray signals in M31.

Abstract

We study the possibility that an extended cosmic-ray leptonic and/or hadronic halo is at the origin of the large-scale gamma-ray emission detected from the Andromeda Galaxy (M31). We consider a broad ensemble of non-homogeneous diffusion scenarios and of cosmic-ray injection sources. We find that cosmic-ray electrons and protons could be, and very likely are, responsible for part, or all, of the gamma-ray emission from M31, including out to more than 100 kpc from the center of the galaxy. We also simulate possible emission from pulsars in M31, and consider the effect of regions of highly inefficient diffusion around cosmic-ray acceleration sites, as suggested by recent TeV halo observations with Cherenkov telescopes.