The Physical Properties of Large-Scale Galactic Filaments
  The characterization of our Galaxy's longest filamentary gas features has
been the subject of several studies in recent years, producing not only a
sizeable sample of large-scale filaments, but also confusion as to whether all
these features (e.g. "Bones", "Giant Molecular Filaments") are the same. They
are not. We undertake the first standardized analysis of the physical
properties ($\rm{H_2}\;$column densities, dust temperatures, morphologies,
radial column density profiles) and kinematics of large-scale filaments in the
literature. We expand and improve upon prior analyses by using the same data
sets, techniques, and spiral arm models to disentangle the filaments' inherent
properties from selection criteria and methodology. Our results suggest that
the myriad filament finding techniques are uncovering different physical
structures, with length ($11-269\,\rm\,pc$), width ($1-40\,\rm\,pc$), mass
($\rm3\times10^3\; M_\odot-1.1\times10^{6}\;M_\odot$), aspect ratio
(3:1-117:1), and high column density fraction ($0.2-100\%$) varying by over an
order of magnitude across the sample of 45 filaments. We develop a radial
profile fitting code, $\texttt{RadFil}$, which is publicly available. We also
perform a $\textit{position-position-velocity}$ ($\textit{p-p-v}$) analysis on
a subsample and find that while $60-70\%$ lie spatially in the plane of the
Galaxy, only $30-45\%$ concurrently exhibit spatial $\textit{and}$ kinematic
proximity to spiral arms. In a parameter space defined by aspect ratio, dust
temperature, and column density, we broadly distinguish three filament
categories, which could indicate different formation mechanisms or histories.
Highly elongated "Bone-like" filaments show the most potential for tracing
gross spiral structure (e.g. arms, spurs), while other categories could be
large concentrations of molecular gas (GMCs, core complexes).
