Volume 535, November 2011
|Number of page(s)||4|
|Published online||26 October 2011|
Search for high-energy γ-ray emission from galaxies of the Local Group with Fermi/LAT
ISDC Data Centre for Astrophysics, Center for Astroparticle Physics, Observatory of Geneva, University of Geneva, Chemin d’Ecogia 16, 1290 Versoix, Switzerland
2 LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 Place Jules Janssen, 92190 Meudon, France
Received: 20 June 2011
Accepted: 12 September 2011
Context. With the discovery of high-energy γ-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 into cosmic ray acceleration in external galaxies.
Aims. We search for high-energy γ-ray emission from those galaxies in the Local Group that have so far not been investigated: M 81, M 83, IC 342, Maffei 1, Maffei 2, and M 94.
Methods.Fermi/LAT public data from August 4, 2008 to January 1, 2011 were analysed for these galaxies. We compared the results to other starburst and normal galaxies detected so far at high energies: the Magellanic clouds, M 31, and the starburst galaxies M 82 and NGC 253.
Results. No significant detection is found in the data for the sources in our sample, and we derive upper limits on their photon flux. After 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.
Key words: radiation mechanisms: non-thermal / gamma rays: galaxies / cosmic rays
© ESO, 2011
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