Mapping Outflowing Gas in the Fermi Bubbles: a UV Absorption Survey of the Galactic Nuclear Wind

Abstract

Using new ultraviolet (UV) spectra of five background quasars from the Cosmic Origins Spectrograph on the Hubble Space Telescope, we analyze the low-latitude (|b|=20-30 degree) regions of the Fermi Bubbles, the giant gamma-ray emitting lobes at the Galactic Center. We combine these data with previous UV and atomic hydrogen (HI) datasets to build a comprehensive picture of the kinematics and metal column densities of the cool outflowing clouds entrained in the Fermi Bubbles. We find that the number of UV absorption components per sightline decreases as a function of increasing latitude, suggesting that the outflowing clouds become less common with increasing latitude. The Fermi Bubble HI clouds are accelerated up to b~7 degree, whereas when we model the UV Fermi Bubbles clouds deprojected flow velocities, we find that they are flat or even accelerating with distance from the Galactic center. This trend, which holds in both the northern and southern hemispheres, indicates that the nuclear outflow accelerates clouds throughout the Fermi Bubbles or has an acceleration phase followed by a coasting phase. Finally, we note the existence of several blueshifted high-velocity clouds at latitudes exceeding ~30 degree, whose velocities cannot be explained by gas clouds confined to the inside of the gamma-ray defined Fermi Bubbles. These anomalous velocity clouds are likely in front of the Fermi Bubbles and could be remnants from past nuclear outflows. Overall, these observations form a valuable set of empirical data on the properties of cool gas in nuclear winds from star-forming galaxies.

arXiv comment26 pages, 12 figures, Accepted for publication in ApJ

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• The Structure of Multiphase Galactic Winds
• The Impact of Cosmic Rays on Thermal Instability in the Circumgalactic Medium
• X-ray bubbles in the circumgalactic medium of TNG50 Milky Way- and M31-like galaxies: signposts of supermassive black hole activity
• Fermi and eRosita bubbles as relics of the past activity of the Galactic black hole
• The Circumgalactic Medium of Milky Way-like Galaxies in the TNG50 Simulation -- I: Halo Gas Properties and the Role of SMBH Feedback
• Intermediate- and high-velocity clouds in the Milky Way I: covering factors and vertical heights
• Molecular Gas within the Milky Way's Nuclear Wind
• Asymmetric eROSITA bubbles as the evidence of a circumgalactic medium wind
• Chandra large-scale mapping of the Galactic center: Probing high-energy structures around the central molecular zone
• Spatially Resolved Gas Flows Around the Milky Way
• Caught in the Act: A Metal-Rich High-Velocity Cloud in the Inner Galaxy
• Diverse metallicities of Fermi bubble clouds indicate dual origins in the disk and halo
• Fermi bubbles: the collimated outburst needed to explain forward-shock edges
• CO Emission Delineating the Interface between the Milky Way Nuclear Wind Cavity and the Gaseous Disk
• Galactic breeze origin for the Fermi bubbles emission
• Not gone with the Wind: Survival of High-Velocity Molecular Clouds in the Galactic center
• X-rays from a Central "Exhaust Vent" of the Galactic Center Chimney
• Evidence for powerful winds and the associated reverse shock as the origin of the Fermi bubbles
• A Near-Infrared Search for Molecular Gas in the Fermi Bubbles
• A New High-latitude H I Cloud Complex Entrained in the Northern Fermi Bubble
• The role of magnetic fields in shaping $\gamma$-ray emission from the Fermi bubbles
• Modeling Multiphase Galactic Outflows: A Multifluid Moving Mesh Approach
• How is Cold Gas Loaded into Galactic Nuclear Outflows?