THE ASTRONOMICAL JOURNAL      VOLUME 106, NUMBER 3, PAGE 848     SEPTEMBER 1993

          ON THE NATURE OF Mg II ABSORPTION LINE SYSTEMS IN QUASARS

                               M. J. DRINKWATER

     Anglo-Australian Observatory, Coonabarabran, NSW 2357, Australia, and
        Observatoire du Mont Megantic, Universite Laval, Quebec, Canada
                    Electronic mail: mjd@aaocbn.aao.gov.au

                                 R. L. WEBSTER

  School of Physics, University of Melbourne, Parkville, Vic 3052, Australia
               Electronic mail: webster@tauon.ph.unimelb.edu.au

                                 P. A. THOMAS

         MAPS, University of Sussex, Brighton BN1 9QH, United Kingdom
                   Electronic mail: petert@syma.sussex.ac.uk


                                   ABSTRACT

    The results of a large R-band imaging survey of 71 bright (m(V) < 18)
    quasars are presented.  The quasars were chosen from published samples
    which have intermediate resolution optical spectroscopy available, so
    the presence of low redshift Mg II absorption lines can be determined.
    We have searched our data for galaxies close to the line-of-sight to
    the quasars, which we might be able to identify with the absorption
    systems.  We find a high coincidence between galaxies very near the
    line-of-sight and quasars showing absorption systems in their spectra,
    a result consistent with other studies.  These galaxies have a mean
    luminosity of 0.5 L(star) (assuming they lie at the absorption
    redshift).  The distribution of impact parameters between the galaxies
    and the quasars extends with a flat distribution to large radii (> 30
    h^-1 kpc).  This suggests that the absorption systems may not be
    gravitationally bound to the observed galaxies, but may be part of
    larger extended systems.  We also find a significant number of galaxies
    near the line-of-sight to the quasar where no absorption is seen in the
    quasar spectrum.  The selection of our quasars is unbiased with respect
    to galaxies near the line-of-sight, so we can compare the observed
    number of absorption systems to that predicted by a simple model with a
    constant covering factor in Mg II absorbing gas within a maximum radius
    of each detected galaxy.  The model is consistent with a covering
    factor of unity, but allowing for incompleteness in the detection of
    galaxies, the covering factor is less than unity.  The redshifts of the
    galaxies are required to confirm this result.