The Impact of Cosmic Rays on the Kinematics of the Circumgalactic Medium
  We use hydrodynamical simulations of two Milky Way-mass galaxies to
demonstrate the impact of cosmic-ray pressure on the kinematics of cool and
warm circumgalactic gas. Consistent with previous studies, we find that
cosmic-ray pressure can dominate over thermal pressure in the inner 50 kpc of
the circumgalactic medium (CGM), creating an overall cooler CGM than that of
similar galaxy simulations run without cosmic rays. We generate synthetic
sightlines of the simulated galaxies' CGM and use Voigt profile fitting methods
to extract ion column densities, Doppler-b parameters, and velocity centroids
of individual absorbers. We directly compare these synthetic spectral line fits
with HST/COS CGM absorption-line data analyses, which tend to show that
metallic species with a wide range of ionization potential energies are often
kinematically aligned. Compared to the Milky-Way simulation run without cosmic
rays, the presence of cosmic-ray pressure in the inner CGM creates narrower OVI
absorption features and broader SiIII absorption features, a quality which is
more consistent with observational data. Additionally, because the cool gas is
buoyant due to nonthermal cosmic-ray pressure support, the velocity centroids
of both cool and warm gas tend to align in the simulated Milky Way with
feedback from cosmic rays. Our study demonstrates that detailed, direct
comparisons between simulations and observations, focused on gas kinematics,
have the potential to reveal the dominant physical mechanisms that shape the
CGM.
