Kavli Affiliate: Mark Vogelsberger
| First 5 Authors: Angus Beane, Lars Hernquist, Elena D’Onghia, Federico Marinacci, Charlie Conroy
| Summary:
Elongated bar-like features are ubiquitous in galaxies, occurring at the
centers of approximately two-thirds of spiral disks. Due to gravitational
interactions between the bar and the other components of galaxies, it is
expected that angular momentum and matter will redistribute over long (Gyr)
timescales in barred galaxies. Previous work ignoring the gas phase of galaxies
has conclusively demonstrated that bars should slow their rotation over time
due to their interaction with dark matter halos. We have performed a simulation
of a Milky Way-like galactic disk hosting a strong bar which includes a
state-of-the-art model of the interstellar medium and a live dark matter halo.
In this simulation the bar pattern does not slow down over time, and instead
remains at a stable, constant rate of rotation. This behavior has been observed
in previous simulations using more simplified models for the interstellar gas,
but the apparent lack of secular evolution has remained unexplained. We propose
that the gas phase of the disk and the dark matter halo act in concert to
stabilize the bar pattern speed and prevent the bar from slowing down or
speeding up. We find that in a Milky Way-like disk, a gas fraction of only
about 5% is necessary for this mechanism to operate. Our result naturally
explains why nearly all observed bars rotate rapidly and is especially relevant
for our understanding of how the Milky Way arrived at its present state.
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