Studies of absorption lines in the spectra of quasi-stellar objects

The possibility that the narrow-line absorption spectra of QSOs arise in foreground galaxies or in other intervening material is examined in this dissertation. The intervening hypothesis is amenable to both direct and indirect tests, some of which are attempted here. The definitive test of the extrinsic nature of a given absorption system is the direct detection of a galaxy with the correct redshift near the line of sight to the QSO. Such direct tests are only feasible for very low redshift absorption systems; since very few suitable systems are currently known, the a priori probability of success is quite small. Alternatively, indirect tests can be extended to much higher redshifts, but the results are only statistical in nature. The observed distribution of absorption systems provides a suitable test; absorption systems should be uniformly distributed along the line of sight to the QSOs if they are due to extrinsic material. Moreover, this test does not require that the absorbing clouds be associated with galaxies. This study is restricted to low-redshift (z approximately less than 1) absorption systems for the purposes of minimizing (1) redshift-dependent selection effects, (2) the effect of neglecting possible evolution, and (3) the problem of ambiguous line identification. Furthermore, it may be possible to subsequently apply direct tests of the intervening hypothesis to systems detected at lower redshift. Several prevously known low-redshift absorption systems are studied, and in all cases in which the reality of the system is established, the observations are consistent with the conjecture that the absorption occurs in galactic-type H I regions. A homogeneous spectroscopic survey of 52 QSOs is used to study the distribution of absorption systems