The Milky Way's Hot Gas Kinematics: Signatures in Current and Future
  OVII Absorption Line Observations
  Detections of $z \approx$ 0 oxygen absorption and emission lines indicate the
Milky Way hosts a hot ($\sim 10^6$ K), low-density plasma extending $\gtrsim$50
kpc into the Mily Way's halo. Current X-ray telescopes cannot resolve the line
profiles, but the variation of their strengths on the sky constrains the radial
gas distribution. Interpreting the OVII K$\alpha$ absorption line strengths has
several complications, including optical depth and line of sight velocity
effects. Here, we present model absorption line profiles accounting for both of
these effects to show the lines can exhibit asymmetric structures and be
broader than the intrinsic Doppler width. The line profiles encode the hot gas
rotation curve, the net inflow or outflow of hot gas, and the hot gas angular
momentum profile. We show how line of sight velocity effects impact the
conversion between equivalent width and the column density, and provide
modified curves of growth accounting for these effects. As an example, we
analyze the LMC sight line pulsar dispersion measure and OVII equivalent width
to show the average gas metallicity is $\gtrsim 0.6 Z_{\odot}$ and $b$
$\gtrsim$ 100 km s$^{-1}$. Determining these properties offers valuable
insights into the dynamical state of the Milky Way's hot gas, and improves the
line strength interpretation. We discuss future strategies to observe these
effects with an instrument that has a spectral resolution of about 3000, a goal
that is technically possible today.
