Fermi Gamma-ray Space Telescope

On the origin of the gamma-ray emission from the Andromeda galaxy

Xian Hou
(Mattia Di Mauro, Christopher Eckner, on behalf of the Fermi-LAT Collaboration)


Recent observations of gamma rays with the Fermi Large Area Telescope (LAT) have revealed extended emission from the center of the Andromeda galaxy, resembling the Galactic Center Excess (GCE) of the Milky Way. The origin of both emissions is still under debate. In this talk, we will briefly review the current observational status of the emissions including morphological and spectral properties with a focus on the Andromeda galaxy. Possible interpretations will be discussed, such as cosmic ray interactions with the interstellar medium, unresolved population of point sources, and dark matter (DM) annihilation or decay. We will compare the unresolved millisecond pulsar (MSP) interpretation of the GCE and the Andromeda galaxy. Latest studies show that MSPs are more consistent with the GCE, while for the Andromeda galaxy, additional astrophysical sources would be required to account for all the observed emission. We will also include the first result of dark matter search in the Andromeda galaxy using about 10 years LAT data from the Femi-LAT Collaboration, which demonstrates the power of the Andromeda galaxy to constrain DM and in particular to test the DM interpretation of the GCE.