A Comparison of Far IR and HI as Reddening Predictors at High Galactic
  Latitude
  Both the Galactic 21-cm line flux from neutral hydrogen (HI) in interstellar
medium and the far-infrared (FIR) emission from Galactic dust grains have been
used to estimate the strength of Galactic reddening of distant sources. In this
work we use a collection of uniform color distant galaxies as color standards
to determine whether the HI method or the FIR method is superior. We find that
the two methods both produce reasonably accurate maps, but that both show
significant errors as compared to the typical color of the background galaxies.
We find that a mixture of the FIR and HI maps in roughly a 2-to-1 ratio is
clearly superior to either map alone. We recommend that future reddening maps
should use both sets of data, and that well-constructed FIR and HI maps should
both be vigorously pursued.
