A Census of Quasar-Intrinsic Absorption in the Hubble Space Telescope Archive: Systems from High Resolution Echelle Spectra

TL;DR

This study catalogs intrinsic quasar absorption systems at low redshift using Hubble Space Telescope spectra, confirming certain ion-specific properties and analyzing their proximity to quasars.

Contribution

It provides a detailed census of low-redshift intrinsic quasar absorption lines, comparing ion-specific selection effectiveness and proximity effects.

Findings

N V systems are most likely intrinsic based on partial coverage.

C IV and O VI are less effective at indicating intrinsic systems.

There is an excess of absorbers near quasar redshift within 5000 km/s.

Abstract

We present a census of z(abs) < 2, intrinsic (those showing partial coverage) and associated [z(abs) ~ z(em)] 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. (2007) survey of 2 < z(em) < 4 quasars that selects systems using similar techniques. We confirm the existence of so-called "strong N V" intrinsic systems (where the equivalent width of H I Ly alpha is small compared to N V 1238) 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 O VI" systems. From a comparison of partial coverage results as a function of ion, we conclude that systems selected by the N V ion have the highest probability of being intrinsic. By contrast, the C IV and O VI ions are poor selectors. Of the 30 O VI systems tested, only two of the systems in the spectrum on 3C 351 show convincing evidence for partial coverage. However, there is a 3-sigma excess in the number of absorbers near the quasar redshift (|Delta v| <= 5000 km/s) over absorbers at large redshift differences. In at least two cases, the associated O VI systems are known not to arise close to the accretion disk of the quasar.