A Principal component analysis of the diffuse interstellar bands
  We present a principal component analysis of 23 line of sight parameters
(including the strengths of 16 diffuse interstellar bands, DIBs) for a
well-chosen sample of single-cloud sightlines representing a broad range of
environmental conditions. Our analysis indicates that the majority ($\sim$93\%)
of the variations in the measurements can be captured by only four parameters
The main driver (i.e., the first principal component) is the amount of
DIB-producing material in the line of sight, a quantity that is extremely well
traced by the equivalent width of the $\lambda$5797 DIB. The second principal
component is the amount of UV radiation, which correlates well with the
$\lambda$5797/$\lambda$5780 DIB strength ratio. The remaining two principal
components are more difficult to interpret, but are likely related to the
properties of dust in the line of sight (e.g., the gas-to-dust ratio). With our
PCA results, the DIBs can then be used to estimate these line of sight
parameters.
