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Discovery of Optical Line Emission Towards the Fermi Bubbles

Published onJun 01, 2020
Discovery of Optical Line Emission Towards the Fermi Bubbles

Observations with the Wisconsin H-Alpha Mapper (WHAM) reveal Hα and [NII] emission at high velocities associated the biconical gamma-ray and X-ray lobes known as the Fermi Bubbles. We find optical-line components near the same velocities as many ultraviolet absorption line features previously detected in a quasar sightline (PDS 456) that passes through the northern Bubble near l = 10.4, b = +11.2. Combined with the recent discovery of optical line emission at high velocities associated with the bar of the Galaxy (the Tilted Disk), these data can constrain the physical conditions of the ionized ISM in the Galactic Center environment as influenced by the bar and by large scale feedback effects of the supermassive black hole, Sgr A*. Variations in the [NII]/H-Alpha line ratio from the Tilted Disk show evidence of a changing interstellar radiation field that can further be tested using emission lines at velocities consistent with the Fermi Bubbles. Continued observations with WHAM will allow for these high velocity emission features to be spectroscopically mapped, as opposed to requiring sparse, bright background sources when using absorption line spectra.

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