Galactic bulge preferred over dark matter for the Galactic centre gamma-ray excess. (May 2018)

• Record Type: Journal Article
• Authors: Macias, Oscar; Gordon, Chris; Crocker, Roland; Coleman, Brendan; Paterson, Dylan; Horiuchi, Shunsaku; Pohl, Martin
• Is Part Of: Nature astronomy. Volume 2:Number 5(2018)
• Page Start: 387
• Page End: 392
• Publication Date: 2018-05
• Subjects: Astronomy -- Periodicals; 520.5
• DOI: 10.1038/s41550-018-0414-3
• Languages: English
• ISSNs: 2397-3366

Abstract

Abstract An anomalous gamma-ray excess emission has been found in the Fermi Large Area Telescope data1 covering the centre of the Galaxy2, 3 . Several theories have been proposed for this 'Galactic centre excess'. They include self-annihilation of dark-matter particles4, an unresolved population of millisecond pulsars5, an unresolved population of young pulsars6, or a series of burst events7 . Here, we report on an analysis that exploits hydrodynamical modelling to register the position of interstellar gas associated with diffuse Galactic gamma-ray emission. We find evidence that the Galactic centre excess gamma rays are statistically better described by the stellar over-density in the Galactic bulge and the nuclear stellar bulge, rather than a spherical excess. Given its non-spherical nature, we argue that the Galactic centre excess is not a dark-matter phenomenon but rather associated with the stellar population of the Galactic bulge and the nuclear bulge. New hydrodynamical models are used to fit the Fermi-LAT data of the Galactic centre and show that the excess γ-ray emission of the region is better fitted by a non-spherical shape, indicating that it is not caused by dark-matter-related phenomena.