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^\circ \mbox{--}30^\circ $ ) 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 (H I) data sets 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 sight line decreases as a function of increasing latitude, suggesting that the outflowing clouds become less common with increasing latitude. The Fermi Bubble H I clouds are accelerated up to b ∼ 7°, 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°, 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. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program 15339.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2020
- DOI:
- arXiv:
- arXiv:2006.13254
- Bibcode:
- 2020ApJ...898..128A
- Keywords:
-
- Milky Way Galaxy;
- Milky Way evolution;
- High-velocity clouds;
- Galactic center;
- 1054;
- 1052;
- 735;
- 565;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 26 pages, 12 figures, Accepted for publication in ApJ