Andromeda galaxy (M31) represents our nearest large neighbor spiral galaxy with a distance of 785 kpc. Its close proximity allows us to optically resolve its stellar disk and bulge as two separate components. Although M31 spans 3.2º x 1º on the sky in optical light, the determination of its extension in γ rays remains controversial. We analyze about 12 years of Fermi-LAT data using the code skyFACT which combines template fitting and image reconstruction. In this work, we robustly characterize its spectral and morphological properties against systematic uncertainties related to the modeling of the Galactic diffuse emission. We present for the first time a proper comparison of non-nested models describing M31 morphology and show the reconstruction of its γ-ray image in a template-independent way in order to identify its components.
|Reference to paper (DOI or arXiv)