Fermi Large Area Telescope observations of Local Group galaxies: Detection of M31 and search for M33
The Fermi/LAT collaboration

TL;DR
This study uses Fermi LAT data to detect gamma-ray emission from M31, compares it with other Local Group galaxies, and finds correlations between star formation rate and gamma-ray luminosity, providing insights into cosmic ray processes.
Contribution
First detection of gamma-ray emission from M31 with detailed comparison to other Local Group galaxies, revealing correlations with star formation rates.
Findings
Gamma-ray emission detected from M31 at 5sigma significance.
No gamma-ray emission detected from M33, upper limit established.
Gamma-ray luminosity correlates with star formation rate across galaxies.
Abstract
Cosmic rays (CRs) can be studied through the galaxy-wide gamma-ray emission that they generate when propagating in the interstellar medium. The comparison of the diffuse signals from different systems may inform us about the key parameters in CR acceleration and transport. We aim to determine and compare the properties of the CR-induced gamma-ray emission of several Local Group galaxies. We use 2 years of nearly continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to search for gamma-ray emission from M31 and M33. We compare the results with those for the Large Magellanic Cloud, the Small Magellanic Cloud, the Milky Way, and the starburst galaxies M82 and NGC253. We detect a gamma-ray signal at 5sigma significance in the energy range 200 MeV-20 GeV that is consistent with originating from M31. The integral photon flux above…
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