Synthetic Large-Scale Galactic Filaments -- on their Formation, Physical
  Properties, and Resemblance to Observations
  Using a population of large-scale filaments extracted from an AREPO
simulation of a Milky Way-like galaxy, we seek to understand the extent to
which observed large-scale filament properties (with lengths $\gtrsim 100$ pc)
can be explained by galactic dynamics alone. From an observer's perspective in
the disk of the galaxy, we identify filaments forming purely due to galactic
dynamics, without the effects of feedback or local self-gravity. We find that
large-scale Galactic filaments are intrinsically rare, and we estimate that at
maximum approximately one filament per $\rm kpc^{2}$ should be identified in
projection, when viewed from the direction of our Sun in the Milky Way. In this
idealized scenario, we find filaments in both the arm and interarm regions, and
hypothesize that the former may be due to gas compression in the
spiral-potential wells, with the latter due to differential rotation. Using the
same analysis pipeline applied previously to observations, we analyze the
physical properties of large-scale Galactic filaments, and quantify their
sensitivity to projection effects and galactic environment (i.e. whether they
lie in the arm or interarm regions). We find that observed "Giant Molecular
Filaments" are consistent with being non-self-gravitating structures dominated
by galactic dynamics. Straighter, narrower, and denser "Bone-like" filaments,
like the paradigmatic Nessie filament, have similar column densities, velocity
gradients, and Galactic plane heights ($z\approx$ 0 pc) to those in our simple
model, but additional physical effects (such as feedback and self-gravity) must
be invoked to explain their lengths and widths.
