Physical conditions of iron-peak low-ionization lines in the FeLoBAL quasar Q0059-2735

Abstract

ABSTRACT Quasar Q0059–2735, one of the first known iron low-ionization broad-absorption-line quasars (FeLoBAL), has a plethora of outflow absorption features at different velocities. Given multiple outflow systems, their troughs from high-ionization transitions form very wide BAL features, e.g. C iv troughs extend from ∼−1000 to −25 000 km s−1. The troughs from low-ionization transitions show more than 1000 narrow absorption lines (NALs) with velocities from −1000 to −3000 km s−1. These include troughs from iron-peak elements, e.g. Fe ii, Fe iii, Cr ii, Mn ii, Ni ii, and Co ii, which are rarely detected in quasar outflows. Most of these troughs are non-black saturated. We constrain the physical conditions of the NALs by fitting the observed Fe ii and Fe iii absorption troughs. We find that the Fe ii absorption arises from a region with an electron temperature (Te) of ∼8000 K and an electron number density (ne) of ∼108 cm−3. The same model also fits well the troughs from other iron-peak elements. In contrast to the Fe ii lines, Fe iii lines are formed in a hotter region, i.e. Te ∼20 000 K. To fit the Fe ii and Fe iii lines simultaneously in a single photoionized cloud, they require a supersolar iron abundance and/or other heating mechanisms for the Fe iii region. The distance (R) of the outflows to the central quasar is determined to be ∼40 pc. The high-resolution data afforded by the Very Large Telescope (VLT)/UVES observations from 2006 and 2018, along with the narrow lines, allow us to constrain the smallest outflow deceleration in any known quasars.