Recognizing the fingerprints of the Galactic bar: a quantitative
  approach to comparing model (l,v) distributions to observation
  We present a new method for fitting simple hydrodynamical models to the (l,v)
distribution of atomic and molecular gas observed in the Milky Way. The method
works by matching features found in models and observations. It is based on the
assumption that the large-scale features seen in (l,v) plots, such as
ridgelines and the terminal velocity curve, are influenced primarily by the
underlying large-scale Galactic potential and are only weakly dependent on
local ISM heating and cooling processes. In our scheme one first identifies by
hand the features in the observations: this only has to be done once. We
describe a procedure for automatically extracting similar features from simple
hydrodynamical models and quantifying the "distance" between each model's
features and the observations. Application to models of the Galactic Bar region
(|l|<30deg) shows that our feature-fitting method performs better than \chi^2
or envelope distances at identifying the correct underlying galaxy model.
