Gamma-ray image reconstruction of the Andromeda galaxy

TL;DR

This study uses 12 years of Fermi-LAT data to reconstruct the gamma-ray image of Andromeda galaxy, revealing its spatial extension and potential additional emission components with systematic uncertainty analysis.

Contribution

It introduces a template-independent gamma-ray imaging method for M31, demonstrating the galaxy's extended emission and a possible second component.

Findings

Gamma-ray emission extends about 0.3-0.4 degrees in M31.

A second emission component extends to at least 1 degree.

Systematic uncertainties from Galactic foreground modeling are around 2.9%.

Abstract

We analyze about 12 years of Fermi-LAT data in the direction of the Andromeda galaxy (M31). We robustly characterize its spectral and morphological properties against systematic uncertainties related to the modeling of the Galactic diffuse emission. We perform this work by adapting and exploiting the potential of the skyFACT adaptive template fitting algorithm. We reconstruct the gamma-ray image of M31 in a template-independent way, and we show that flat spatial models are preferred by data, indicating an extension of the $\gamma$-ray emission of about 0.3-0.4 degree for the bulge of M31. This study also suggests that a second component, extending to at least 1 degree, contributes to the observed total emission. We quantify systematic uncertainties related to mis-modeling of Galactic foreground emission at the level of 2.9%.