Evidence that 50% of BALQSO Outflows Are Situated at Least 100 pc from the Central Source

Abstract

The most robust way for determining the distance of quasar absorption outflows is the use of troughs from ionic excited states. The column density ratio between the excited and resonance states yields the outflow number density. Combined with a knowledge of the outflow's ionization parameter, a distance from the central source (R) can be determined. Here we report results from two surveys targeting outflows that show troughs from S iv. One survey includes 1091 SDSS and BOSS quasar spectra, and the other includes higher-quality spectra of 13 quasars observed with the Very Large Telescope. Our S iv samples include 38 broad absorption line (BAL) outflows, and four mini-BAL outflows. The S iv is formed in the same physical region of the outflow as the canonical outflow-identifying species C iv. Our results show that S iv absorption is only detected in 25% of C iv BAL outflows. The smaller detection fraction is due to the higher total column density (N H ) needed to detect S iv absorption. Since R empirically anti-correlates with N H the results of these surveys can be extrapolated to C iv quasar outflows with lower N H as well. We find that at least 50% of quasar outflows are at distances larger than 100 pc from the central source, and at least 12% are at distances larger than 1000 pc. These results have profound implications to the study of the origin and acceleration mechanism of quasar outflows and their effects on the host galaxy.

Stratified disc wind models for the AGN broad-line region: ultraviolet, optical, and X-ray properties

“…It is worth noting that, in a general sense, the question of scale is a difficult one for physical models of AGN. BAL outflow distances in excess of 100 pc have been inferred from density-sensitive lines (Borguet et al 2012;Chamberlain et al 2015;Arav et al 2018). This is significantly larger than expected from disc wind theory or simulations and may require alternative scenarios involving shocks or cloud disruption (Faucher-Giguére et al 2012;Zeilig Hess et al 2019).…”

HST/COS Observations of Quasar Outflows in the 500–1050 Å Rest Frame. I. The Most Energetic Outflows in the Universe and Other Discoveries

“…A comparative discussion of all the methods (found in the literature) that are used to determine R is given in Arav et al (2018)'s section 7.1. The EUV500 includes several transitions from excited states of abundant high-ionization species (e.g., O iii, iv, and v; and Ne v and vi, see figure 1), which produce troughs in most high-ionization outflows.…”

“…An alternative method for determining n e is via a photoionization time-scale analysis (this time-scale is inversely proportional to the n e of the outflow; see Arav et al 2015). However, this method is both resource intensive (many observational epochs are needed) and is model-dependent (see the discussion in section 7.1 of Arav et al 2018)…”

On the emergence of thousands of absorption lines in the quasar PG 1411+442: a clumpy high-column density outflow from the broad emission-line region?

“…Some observational studies report small distances consistent with this picture (e.g., Wampler et al 1995;De Kool et al 2002a;Hall et al 2011;Capellupo et al 2013;Zhang et al 2015b;Muzahid et al 2016;Shi et al 2016a;Moravec et al 2017;Hamann et al 2018, and refs. therein), while others derive much larger radial distances up to several kpc (de Kool et al 2001;Moe et al 2009;Dunn et al 2010;Arav et al 2018). The wide range in reported radial distances, R, is important for feedback considerations because the derived outflow masses and kinetic energies scale like R 2 , while the kinetic energy rates (divided by an average flow time R/v) scale like R (e.g., Moravec et al 2017).…”