The Fermi Bubbles: Gamma-ray, Microwave, and Polarization Signatures of Leptonic AGN Jets

Abstract

The origin of the Fermi bubbles and the microwave haze is yet to be determined. To disentangle different models requires detailed comparisons between theoretical predictions and multi-wavelength observations. Our previous simulations have demonstrated that the primary features of the Fermi bubbles could be successfully reproduced by recent jet activity from the central active galactic nucleus (AGN). In this work, we generate gamma-ray and microwave maps and spectra based on the simulated properties of cosmic rays (CRs) and magnetic fields in order to examine whether the observed bubble and haze emission could be explained by leptons contained in the AGN jets. We also investigate the model predictions of the polarization properties of the Fermi bubbles. We find that: (1) The same population of leptons can simultaneously explain the bubble and haze emission given that the magnetic fields within the bubbles are very close to the exponentially distributed ambient field, which can be explained by mixing in of the ambient field followed by turbulent field amplification; (2) The centrally peaked microwave profile suggests CR replenishment, which is consistent with the presence of a more recent second jet event; (3) The bubble interior exhibits a high degree of polarization because of ordered radial magnetic field lines stretched by elongated vortices behind the shocks; highly-polarized signals could also be observed inside the draping layer; (4) Enhancement of rotation measures could exist within the shock-compressed layer because of increased gas density and more amplified and ordered magnetic fields. We discuss the possibility that the deficient haze emission at b<-35 degrees is due to the suppression of magnetic fields, which is consistent with the existence of lower-energy CRs causing the polarized emission at 2.3 GHz. Possible AGN jet composition in the leptonic scenario is also discussed.

15 pages, 9 figures, matched with MNRAS published version

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• Galactic Neutrinos in the TeV to PeV Range
• The Interaction of the Fermi Bubbles with the Milky Way's Hot Gas Halo
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• The Spatially Uniform Spectrum of the Fermi Bubbles: the Leptonic AGN Jet Scenario
• Unveiling the Origin of the Fermi Bubbles
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• The Accretion Wind Model of the Fermi Bubbles (II): Radiation
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• Very-high energy observations of the Galactic center region by VERITAS in 2010-2012
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• Steady-State Hadronic Gamma-Ray Emission from 100-Myr-Old Fermi Bubbles
• Multi-wavelength Emission from the Fermi Bubble I. Stochastic acceleration from Background Plasma
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• A Supernova-driven, Magnetically-collimated Outflow as the Origin of the Galactic Center Radio Bubbles
• A Latitude-Dependent Analysis of the Leptonic Hypothesis for the Fermi Bubbles
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• Stress-Testing Cosmic Ray Physics: The Impact of Cosmic Rays on the Surviving Disk of Ram Pressure Stripped Galaxies
• The Fermi bubbles from stochastic acceleration of electrons in a Galactic outflow
• On the origin of the central 1" hole in the stellar disk of Sgr A* and the Fermi gamma-ray bubbles
• The population of Galactic centre filaments III: candidate radio and stellar sources
• Fermi bubbles: high latitude X-ray supersonic shell
• Evolution of Primordial Neutrino Helicities in Astrophysical Magnetic Fields and Implications for their Detection
• The spectral index of polarized diffuse Galactic emission between 30 and 44 GHz
• Metal Enrichment in the Fermi Bubbles as a Probe of Their Origin
• Emission from hadronic and leptonic processes in galactic jet-driven bubbles
• The Bending Feature of the Fermi Bubbles: A Presumed Horizontal Galactic Wind and Its Implication on the Bubbles' Age
• Effects of Anisotropic Viscosity on the Evolution of Active Galactic Nuclei Bubbles in Galaxy Clusters
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• Not gone with the Wind: Survival of High-Velocity Molecular Clouds in the Galactic center
• The AGN Jet Model of the Fermi Bubbles
• Possible counterpart signal of the Fermi bubbles at the cosmic-ray positrons
• Fermi-bubble bulk and edge analysis reveals dust, cooling breaks, and cosmic-ray diffusion, facilitating a self-consistent model
• Multi-wavelength emission from leptonic processes in ageing galaxy bubbles
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• Supermassive black holes and their surroundings: MeV signatures
• Diffuse continuum emission and large extended sources at MeV energies
• The role of magnetic fields in shaping $\gamma$-ray emission from the Fermi bubbles