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Search for 511 keV emission in satellite galaxies of the Milky Way with INTEGRAL/SPI


Siegert, T and Diehl, R and Vincent, AC and Guglielmetti, F and Krause, MGH and Boehm, C, Search for 511 keV emission in satellite galaxies of the Milky Way with INTEGRAL/SPI, Astronomy and Astrophysics, 595 Article A25. ISSN 0004-6361 (2016) [Refereed Article]


Copyright Statement

Copyright 2016 ESO

DOI: doi:10.1051/0004-6361/201629136


The positron annihilation gamma-ray signal in the Milky Way (MW) shows a puzzling morphology: a very bright bulge and a very low surface-brightness disk. A coherent explanation of the positron origin, propagation through the Galaxy and subsequent annihilation in the interstellar medium has not yet been found. Tentative explanations involve positrons from radioactivity, X-ray binaries, and dark matter (DM). Dwarf satellite galaxies (DSGs) are believed to be DM-dominated and hence promising candidates in the search for 511 keV emission as a result of DM annihilation into electron-positron pairs. The goal of this study is to constrain possible 511 keV gamma-ray signals from 39 DSGs of the MW and to test the annihilating DM scenario. We use the spectrometer SPI on INTEGRAL to extract individual spectra for the studied objects. As the diffuse galactic emission dominates the signal, the large scale morphology of the MW has been modelled accordingly and was included in a maximum likelihood analysis. Alternatively, a distance-weighted stacked spectrum has been determined. Only Reticulum II (Ret II) shows a 3.1 sigma signal. Five other sources show tentative 2 sigma signals. The mass-to-511-keV-luminosity-ratio shows a marginal trend towards higher values for intrinsically brighter objects, opposite to the V band mass-to-light-ratio, which is generally used to uncover DM in DSGs. All derived flux values are above the level implied by a DM interpretation of the MW bulge signal. The signal from Ret II is unlikely to be related to a DM origin alone, otherwise, the MW bulge would be about 100 times brighter than what is seen. Ret II is exceptional considering the DSG sample, and rather points to enhanced recent star formation activity, if its origins are similar to processes in the MW. Understanding this emission may provide further clues regarding the origin of the annihilation emission in the MW.

Item Details

Item Type:Refereed Article
Research Division:Physical Sciences
Research Group:Astronomical and Space Sciences
Research Field:Cosmology and Extragalactic Astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Physical Sciences
Author:Krause, MGH (Dr Martin Krause)
ID Code:115118
Year Published:2016
Deposited By:Mathematics and Physics
Deposited On:2017-03-08
Last Modified:2017-04-03
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