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20 April 2024 |
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Probing the Fermi Bubbles in Ultraviolet Absorption: A Spectroscopic Signature of the Milky Way's Biconical Nuclear Outflow | | Andrew J. Fox
; Rongmon Bordoloi
; Blair D. Savage
; Felix J. Lockman
; Edward B. Jenkins
; Bart P. Wakker
; Joss Bland-Hawthorn
; Svea Hernandez
; Tae-Sun Kim
; Robert A. Benjamin
; David V. Bowen
; Jason Tumlinson
; | | Date: |
3 Dec 2014 | | Abstract: | Giant lobes of plasma extend 55 degrees above and below the Galactic Center,
glowing in emission from gamma rays (the Fermi Bubbles) to microwaves (the WMAP
haze) and polarized radio waves. We use ultraviolet absorption-line spectra
from the Hubble Space Telescope to constrain the velocity structure of the
outflowing gas within these regions, targeting the quasar PDS 456 (Galactic
coordinates l,b=10.4, +11.2 degrees). This sightline passes through a clear
biconical structure seen in hard X-ray and gamma-ray emission near the base of
the northern Fermi Bubble. We report two high-velocity metal absorption
components, at v_LSR=-235 and +250 km/s, which cannot be explained by
co-rotating gas in the Galactic disk or halo. Their velocities are suggestive
of an origin on the front and back side of an expanding biconical outflow
emanating from the Galactic Center. We develop simple kinematic biconical
outflow models that can explain these observed profiles with an outflow
velocity of ~900 km/s and a full opening angle of ~110 degrees (matching the
X-ray bicone). This indicates Galactic Center activity over the last ~2.5-4.0
Myr, in line with age estimates of the Fermi Bubbles. The observations
illustrate the use of UV absorption-line spectroscopy to probe the properties
of swept-up gas venting into the Fermi Bubbles. | | Source: | arXiv, 1412.1480 | | Services: | Forum | Review | PDF | Favorites | |
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