H I, galaxy counts, and reddening - Variation in the gas-to-dust ratio, the extinction at high galactic latitudes, and a new method for determining galactic reddening

The interrelationships among Shane-Wirtanen (1967) galaxy counts, H I column densities, and reddenings are reanalyzed, and many of the problems raised by Heiles (1976) are resolved. These problems were caused by two factors: subtle biases in the reddening data and a variable gas-to-dust ratio in the galaxy. A compilation of reddenings for RR Lyrae stars and globular clusters which are on the same system and which are believed to be relatively free of biases is presented. The extinction at the galactic poles, as determined by galaxy counts, is reexamined by using a new method to analyze galaxy counts. This method partially accounts for the nonrandom clustering of galaxies and permits a reasonable estimate of the error in log N(gal) as a function of latitude. The analysis shows that galaxy counts (or galaxy cluster counts) are too noisy to allow direct determination of the extinction or the variation in extinction near the galactic poles. From all available data it is concluded that the reddening at the poles is small and irregularly distributed. It is found that there are zero offsets in the relations between E(B-V) and H I, and between galaxy counts and H I, which are at least partly the result of an instrumental effect in the radio data.