HST and ground-based spectroscopy of quasar outflows: from mini-BALs to BALs

Abstract

Quasar outflows have been posited as a mechanism to couple supermassive black holes to evolution in their host galaxies. We use multi-epoch spectra from the Hubble Space Telescope (HST) and ground-based observatories to study the outflows in seven quasars that have C iv outflow lines ranging from a classic broad absorption line (BAL) to weaker/narrower ‘mini-BALs’ across rest wavelengths of at least 850–1650 Å. The C iv outflow lines all varied within a time frame of ≤1.9 yr (rest). This includes equal occurrences of strengthening and weakening plus the emergence of a new BAL system at −38 800 km s−1 accompanied by dramatic strengthening in a mini-BAL at −22 800 km s−1. We infer from ∼1:1 doublet ratios in P v and other lines that the BAL system is highly saturated with line-of-sight covering fractions ranging from 0.27 to 0.80 in the highest to lowest column density regions, respectively. Three of the mini-BALs also provide evidence for saturation and partial covering based on ∼1:1 doublet ratios. We speculate that the BALs and mini-BALs form in similar clumpy/filamentary outflows, with mini-BALs identifying smaller or fewer clumps along our lines of sight. If we attribute the line variabilities to clumps crossing our lines of sight at roughly Keplerian speeds, then a typical variability time in our study, ∼1.1 yr, corresponds to a distance ∼2 pc from the central black hole. Combining this with the speed and minimum total column density inferred from the P v BAL, NH ≳ 2.5 × 1022 cm−2, suggests that the BAL outflow kinetic energy is in the range believed to be sufficient for feedback to galaxy evolution.