Accurate galactic N(H) values towards quasars and AGN

We have measured integrated Galactic 21 cm column densities toward ~174 quasars and active galactic nuclei using the NRAO 140 ft telescope at Green Bank. These data have been corrected for stray radiation with the technique of Lockman et al. (1986). The 21 arcmin beam size of the 140 ft is small enough to minimize the uncertainty in N_H_ due to angular variations in the H I of the Galaxy at high latitudes. The resulting column densities are accurate to ~1 X 10^19^ atoms cm^-2^ or ~5%, whichever error is larger. Opacity uncertainties dominate the errors above N_H_ ~4 X 10^20^ atoms cm^-2^.

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