A Hubble Space Telescope Faint Object Spectrograph Survey for Broad Absorption Lines in a Sample of Low-Redshift Weak [O iii] Quasi-stellar Objects

Details A Hubble Space Telescope Faint Object Spectrograph Survey for Broad Absorption Lines in a Sample of Low-Redshift Weak [O iii] Quasi-stellar Objects A Hubble Space Telescope Faint Object Spectrograph Survey for Broad Absorption Lines in a Sample of Low-Redshift Weak [O iii] Quasi-stellar Objects

Feb 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...476...40t&link_type=abstract

Astrophysical Journal v.476, p.40

Astronomy and Astrophysics

Astronomy

51

Galaxies: Structure, Galaxies: Quasars: Absorption Lines, Galaxies: Quasars: Emission Lines

Scientific paper

The study by Boroson & Meyers led to the suggestion that radio-quiet QSOs with weak [O III] and strong Fe II emission spectra form a class of QSOs that has a high probability of exhibiting broad absorption lines (BALs) in their spectra. Furthermore, they argued that since narrow-line [O III] emission is almost certainly emitted isotropically, this indicates that such objects have relatively large BAL region covering factors. Low covering factor models are consistent with scenarios in which most QSOs have BAL regions, while higher covering factor models are consistent with scenarios in which there are special classes of QSOs with large BAL region outflows. By making Hubble Space Telescope (HST) FOS observations and using IUE or HST archival data when available, the details of the Boroson & Meyers suggestion have been explored by directly searching for classical C IV BALs in a sample of 18 QSOs with weak [O III] and often strong Fe II emission. Six of the 18 QSOs are found to exhibit C IV BALs. (In the archival sample, four of six objects have BALs, while two of the 12 new objects observed with the HST FOS have BALs.) However, there is evidence that the sample is heterogeneous, with IRAS-selected objects and high-luminosity objects having a greater tendency to exhibit BALs. If an isotropic model for [O III] emission equivalent width is considered, the results suggest that for the 18 object sample as a whole the average BAL region covering factor is ~0.33 ^{+0.20}_{-0.09} , which is significantly larger (with a more than 99% probability) than the overall fraction of QSOs observed to have BALs (normally taken as ~0.1). Given possible selection effects, in the context of an isotropic model the results may indicate that some of the sample objects have covering factors <<0.33, while others have covering factors >>0.33. At the same time, it is impossible to rule out in a non--model-dependent way a scenario in which orientation effects are important and covering factors are generally small. Results such as these ultimately provide constraints on QSO geometries, intrinsic QSO properties, and evolutionary processes in QSOs.

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