We present a census of zabs≃2 intrinsic (those showing partial coverage) and associated (zabs ~ zem) quasar absorption-line systems detected in the Hubble Space Telescope archive of Space Telescope Imaging Spectrograph echelle spectra. This work complements the Misawa et al. survey of 2<zem<4 quasars that selects systems using similar techniques.We confirm the existence of so-called strong NV intrinsic systems (where the equivalent width of HI Lyα is small compared to NV λ1238) presented in that work, but find no convincing cases of 'strong C IV' intrinsic systems at low redshift/luminosity. Moreover, we also report on the existence of 'strong OVI' systems. From a comparison of partial coverage results as a function of ion, we conclude that systems selected by the NV ion have the highest probability of being intrinsic. By contrast, the C IV and OVI ions are poor selectors. Of the 30 OVI systems tested, only two of the systems in the spectrum on 3C 351 show convincing evidence for partial coverage. However, there is an ~3s excess in the number of absorbers near the quasar redshift (|δv|≤ 5000 km s-1) over absorbers at large redshift differences. In at least two cases, the associated OVI systems are known not to arise close to the accretion disc of the quasar.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science