Astronomy and Astrophysics – Astrophysics – High Energy Astrophysical Phenomena
Scientific paper
2011-09-15
Astronomy and Astrophysics
Astrophysics
High Energy Astrophysical Phenomena
5 pages, 2 figures, 1 table; accepted for publication in A&A; language corrected
Scientific paper
10.1051/0004-6361/201117523
With the discovery of high energy {\gamma}-ray emission from the Andromeda galaxy (M 31) by the Fermi/LAT collaboration, normal galaxies begin to arise from the shadows for the first time, providing insight on cosmic ray acceleration in external galaxies. We search for high energy {\gamma}-ray emission from galaxies in the Local Group which were not investigated so far: M 81, M 83, IC 342, Maffei 1, Maffei 2 and M 94. Fermi/LAT public data from August 4, 2008 to January 1, 2011 were analysed for these galaxies. We compare the results to other starburst and normal galaxies detected at high energies so far: the Magellanic clouds, M 31, and the starburst galaxies M 82 and NGC 253. No significant detection is found in the data for the sources in our sample, and we derive upper limits on their photon flux. Comparing the results to other Local Group objects, we find that the derived upper limits are fully compatible with expectations from cosmic rays interacting with the interstellar medium within the host galaxies. In the case of M 33 and M 83, a detection in Fermi/LAT data should be imminent. The expected fluxes for the other sources in the sample are below the sensitivity of Fermi/LAT, even after 10 years of observation. Collective emission from compact objects in the host galaxies is also found to be negligible compared to the expected emission from cosmic ray interactions.
Lenain Jean-Philippe
Walter Roland
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