Metal Enrichment in the Fermi Bubbles as a Probe of Their Origin

Abstract

The Fermi bubbles are gigantic gamma-ray structures in our Galaxy. The physical origin of the bubbles is still under debate. The leading scenarios can be divided into two categories. One is the nuclear star forming activity similar to extragalactic starburst galaxies and the other is the past active galactic nucleus (AGN) like activity of the Galactic center supermassive black hole. In this paper, we propose that metal abundance measurements will provide an important clue to probe their origin. Based on a simple spherically symmetric bubble model, we find that the generated metallicity and abundance pattern of the bubbles' gas strongly depend on assumed star formation or AGN activities. Star formation scenarios predict higher metallicities and abundance ratios of [O/Fe] and [Ne/Fe] than AGN scenarios do because of supernovae ejecta. Furthermore, the resultant abundance depends on the gamma-ray emission process because different mass injection histories are required for the different gamma-ray emission processes due to the acceleration and cooling time scales of non-thermal particles. Future X-ray missions such as ASTRO-H and Athena will give a clue to probe the origin of the bubbles through abundance measurements with their high energy resolution instruments.

6 pages, 1 figure, accepted for publication in PASJ

References in corpus (13)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Galactic chemical evolution: Carbon through Zinc
• The power of blazar jets
• The Spectrum and Morphology of the Fermi Bubbles
• The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays
• Extended Anomalous Foreground Emission in the WMAP 3-Year Data
• Giant Magnetized Outflows from the Centre of the Milky Way
• Fermi Bubbles Inflated by Winds Launched from the Hot Accretion Flow in Sgr A*
• X-ray and UV spectroscopy of Galactic diffuse hot gas along the LMC X--3 sight line
• Revealing Type Ia supernova physics with cosmic rates and nuclear gamma rays
• A Hadronic-Leptonic Model for the Fermi Bubbles: Cosmic-Rays in the Galactic Halo and Radio Emission
• High Resolution X-ray Spectroscopy of the Local Hot Gas along the 3C 273 Sightline
• Structual Study of Galactic Hot Gas toward Markarian 421 from X-Ray Absorption and Emission Lines

Cited by in corpus (4)

• The Interaction of the Fermi Bubbles with the Milky Way's Hot Gas Halo
• Interaction of the Galactic-Centre Super Bubbles with the Gaseous Disc
• A magnetised Galactic halo from inner Galaxy outflows
• Evidence for powerful winds and the associated reverse shock as the origin of the Fermi bubbles