Associated Absorption Lines in the Radio‐loud Quasar 3C 351: Far‐Ultraviolet Echelle Spectroscopy from theHubble Space Telescope

Abstract

As one of the most luminous radio-loud quasars showing intrinsic ultraviolet (UV) and X-ray absorption, 3C 351 provides a laboratory for studying the kinematics and physical conditions of such ionized absorbers. We present an analysis of the intrinsic absorption lines in the high-resolution (~7 km s-1) far-UV spectrum that was obtained from observations with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. The spectrum spans wavelengths from 1150 to 1710 A and shows strong emission lines from O VI and Lyα. Associated absorption lines are present on the blue wings of the high-ionization emission doublets O VI λλ1032, 1038 and N V λλ1238, 1242, as well as the Lyman lines through Ly. These intrinsic absorption features are resolved into several distinct kinematic components, covering rest-frame velocities from -40 to -2800 km s-1, with respect to the systemic redshift of zem = 0.3721. For the majority of these absorption-line regions, strong evidence of partial covering of both the background continuum source and the broad emission line region is found, which supports the intrinsic absorption origin and rules out the possibility that the absorption arises in some associated cluster of galaxies. The relationship between the far-UV absorbers and X-ray warm absorbers is studied with the assistance of photoionization models. Most of the UV-associated absorption components have low values of the ionization parameter and total hydrogen column densities, which is inconsistent with previous claims that the UV and X-ray absorption arises in the same material. Analysis of these components supports a picture with a wide range of ionization parameters, temperatures, and column densities in active galactic nucleus outflows.