PoS - Proceedings of Science
Volume 358 - 36th International Cosmic Ray Conference (ICRC2019) - GRD - Gamma Ray Direct
Fermi-LAT Observations of Gamma-Ray Emission Towards the Outer Halo of M31
C. Karwin,* S. Murgia, S. Campbell, I. Moskalenko
*corresponding author
Full text: pdf
Pre-published on: July 22, 2019
Published on:
The Andromeda galaxy is the closest spiral galaxy to us and has been the subject of numerous studies. It harbors a massive dark matter halo which may span up to ~600 kpc across and comprises ~90% of the galaxy's total mass. This halo size translates into a large diameter of 42 degrees on the sky for an M31-Milky Way (MW) distance of 785 kpc, but its presumably low surface brightness makes it challenging to detect with gamma-ray telescopes. Using 7.6 years of Fermi Large Area Telescope (Fermi-LAT) observations, we make a detailed study of the gamma-ray emission between 1-100 GeV towards M31's outer halo, with a total field radius of 60 degrees centered at M31, and perform an in-depth analysis of the systematic uncertainties related to the observations. We use the cosmic ray propagation code GALPROP to construct specialized interstellar emission models to characterize the foreground gamma-ray emission from the MW, including a self-consistent determination of the isotropic component. We find evidence for an extended excess that appears to be distinct from the conventional MW foreground, having a total radial extension upwards of ~120-200 kpc from the center of M31. We discuss plausible interpretations of the excess emission but emphasize that uncertainties in the MW foreground, and in particular, modeling of the H I-related components, have not been fully explored and may impact the results.
DOI: https://doi.org/10.22323/1.358.0570
How to cite

Metadata are provided both in "article" format (very similar to INSPIRE) as this helps creating very compact bibliographies which can be beneficial to authors and readers, and in "proceeding" format which is more detailed and complete.

Open Access
Creative Commons LicenseCopyright owned by the author(s) under the term of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.