THE ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 105:369-373, 1996 August

            GALACTIC H I COLUMN DENSITIES TOWARD QUASARS AND ACTIVE
                                GALACTIC NUCLEI

                               EDWARD M. MURPHY
       University of Virginia and National Radio Astronomy Observatory,
                 520 Edgemont Road, Charlottesville, VA 22903

                               FELIX J. LOCKMAN
          National Radio Astronomy Observatory, Green Bank, WV 24944

                                   ARI LAOR
               Physics Department, Technion, Haifa 32000, Israel

                                      AND

                                 MARTIN ELVIS
       Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138


                                   ABSTRACT

        We have determined accurate values of the Galactic neutral hydrogen
     column density, N_H, toward 220 quasars and active galactic nuclei
     from 21 cm H I measurements made on the 130 Foot Telescope (42.7 m).
     Accurate values of N_H have now been obtained for the whole PG bright
     quasar sample and most quasars that have been observed by ROSAT and
     the Hubble Space Telescope through mid-1993.  The spectra were
     corrected for stray 21 cm radiation yielding values of N_H with a
     typical uncertainty of 1x10^19 cm^-2 for high Galactic latitude
     directions.  The H I column densities will be useful for correcting
     for interstellar opacity at UV and soft X-ray wavelengths, and for
     estimating the reddening and extinction toward these objects.

     Subject headings: Galaxy: structure -- radio lines: ISM -- X-rays:
                       general