A Multiwavelength View of a Mass Outflow from the Galactic Center

Abstract

The Galactic center (GC) lobe is a degree-tall shell of gas that spans the central degree of our Galaxy. It has been cited as evidence for a mass outflow from our GC region, which has inspired diverse models for its origin. However, most work has focused on the morphology of the GC lobe, which has made it difficult to draw strong conclusions about its nature. Here, I present a coherent, multiwavelength analysis of new and archival observations of the GC lobe. Radio continuum emission shows that the GC lobe has a magnetized layer with a diameter of 110 pc and an equipartition field strength ranging from 40 to 100 $\mu$G. Recombination line emission traces an ionized shell nested within the radio continuum with diameter of 80 pc and height 165 pc. Mid-infrared maps at 8 and 15 $\mu$m show that the GC lobe has a third layer of warm dust and PAH-emission that surrounds the radio continuum shell with a diameter of 130 pc. Assuming adiabatic expansion of the gas in the GC lobe, its formation required an energy input of about $5\times 10^{52}$ ergs. I compare the physical conditions of the GC lobe to several models and find best agreement with the canonical starburst outflow model. The formation of the GC lobe is consistent with the currently observed pressure and star formation rate in the central tens of parsecs of our Galaxy. Outflows of this scale are more typical of dwarf galaxies and would not be easily detected in nearby spiral galaxies. Thus, the existence of such an outflow in our own Galaxy may indicate that it is relatively common phenomenon in the nuclei of spiral galaxies. (Abridged)

Accepted to ApJ. 15 pages, 8 (compressed) figures

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• Nonthermal particles and photons in starburst regions and superbubbles
• Non-Thermal Insights on Mass and Energy Flows Through the Galactic Centre and into the Fermi Bubbles
• The HIPASS survey of the Galactic plane in Radio Recombination Lines
• Cosmic rays and the magnetic field in the nearby starburst galaxy NGC253 III. Helical magnetic fields in the nuclear outflow
• Discovery of the recombining plasma in the south of the Galactic center; a relic of the past Galactic center activity?
• The ATCA HI Galactic Center Survey
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• Gamma-Rays and the Far-Infrared-Radio Continuum Correlation Reveal a Powerful Galactic Centre Wind
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• The Galactic Center Lobe Filled with Thermal Plasma
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