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.

26 pages, 12 figures, Accepted for publication in ApJ

References in corpus (14)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• The Spectrum and Morphology of the Fermi Bubbles
• Extended Anomalous Foreground Emission in the WMAP 3-Year Data
• Giant Magnetized Outflows from the Centre of the Milky Way
• Star Formation in the Central 400 pc of the Milky Way: Evidence for a Population of Massive YSOs
• Probing the Fermi Bubbles in Ultraviolet Absorption: A Spectroscopic Signature of the Milky Way's Biconical Nuclear Outflow
• Fermi Bubbles Inflated by Winds Launched from the Hot Accretion Flow in Sgr A*
• Nuclear Outflow of the Milky Way: Studying the Kinematics and Spatial Extent of the Northern Fermi Bubble
• The Interaction of the Fermi Bubbles with the Milky Way's Hot Gas Halo
• Does the Milky Way Produce a Nuclear Galactic Wind?
• The large-scale ionization cones in the Galaxy
• The High Velocity Gas toward Messier 5: Tracing Feedback Flows in the Inner Galaxy
• Observation of Acceleration of HI Clouds Within the Fermi Bubbles