Abstract
We have searched for an extended high-energy gamma-ray emission around the nearby giant spiral Andromeda galaxy M31 using almost 7 years of Fermi LAT data at energies above 300 MeV. The presence of a diffuse gamma-ray halo with total photon flux 2.6±0.6×10 −9 cm −2 s −1 , corresponding to a luminosity (0.3-100 GeV) of (3.2±0.6)×10 38 erg s −1 (for a distance of 780 kpc) was found at a 5.3σ confidence level. The best-fit halo template corresponds to two 6-7.5 kpc bubbles symmetrically located perpendicular to the M31 galactic disc, similar to the 'Fermi bubbles' found around the Milky Way centre.
Highlights
There are several observational manifestations of extended baryonic coronae around spiral galaxies: soft diffuse X-ray emission extending up to several ten kpc from the central galaxy [1], absorption in O VII line [2, 3], distortions in the shape of gas clouds [4] and stripping of gas in the satellite galaxies by the ram-pressure of the halo gas [5], see [6] and references therein for a review
We searched for diffuse gamma-ray emission from the M31 galaxy
The galaxy was modelled in two different ways: as a point-like source or as an extended object
Summary
There are several observational manifestations of extended baryonic coronae around spiral galaxies: soft diffuse X-ray emission extending up to several ten kpc from the central galaxy [1], absorption in O VII line [2, 3], distortions in the shape of gas clouds [4] and stripping of gas in the satellite galaxies by the ram-pressure of the halo gas [5], see [6] and references therein for a review Such a hot halo around the Milky Way is established by several different methods [7]. For further details of analysis, see [15]
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