Metallicities of Outflowing Fermi Bubble Clouds

The Fermi Bubbles are an example of nuclear feedback in our own Milky Way. The bubble’s proximity and thus large angular extent on the sky (±50° in latitude and ±20° in longitude) allows us to study the effects of a nuclear outflow on its host galaxy in greater detail than is possible in any other galaxy. Clouds detected in the UV towards the Fermi Bubbles have traditionally been assumed to be launched from the Milky Way disk into the bubbles. However, the origin of these UV-detected Fermi Bubbles clouds has never been confirmed. We use existing Fermi Bubble FUV surveys along with new and existing atomic hydrogen data to create the first Fermi Bubble cloud metallicity survey. We find that Fermi Bubble clouds have a large range of metallicities from <20% solar to super-solar indicating that they have two origins: the Galactic disk and halo. These results imply that the Fermi bubbles simultaneously remove gas from the Galactic disk and sweep up Galactic halo gas as they expand.