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Fermi-LAT Observations of γ-Ray Emission toward the Outer Halo of M31.
- Source :
- Astrophysical Journal; 8/1/2019, Vol. 880 Issue 2, p1-1, 1p
- Publication Year :
- 2019
-
Abstract
- 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° 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 γ-ray telescopes. Using 7.6 yr of Fermi Large Area Telescope (Fermi–LAT) observations, we make a detailed study of the γ-ray emission between 1–100 GeV toward M31's outer halo, with a total field radius of 60° 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 γ-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 upward 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. [ABSTRACT FROM AUTHOR]
- Subjects :
- ANDROMEDA Galaxy
COSMIC background radiation
DARK matter
SPIRAL galaxies
TELESCOPES
Subjects
Details
- Language :
- English
- ISSN :
- 0004637X
- Volume :
- 880
- Issue :
- 2
- Database :
- Complementary Index
- Journal :
- Astrophysical Journal
- Publication Type :
- Academic Journal
- Accession number :
- 137904453
- Full Text :
- https://doi.org/10.3847/1538-4357/ab2880