A physical model of FeLoBALs: implications for quasar feedback

Abstract

Photoionization modelling of the low‐ionization broad absorption lines of certain quasars, known as FeLoBALs, has recently revealed the number density of the wind absorbers and their distance from the central supermassive black hole. From these, the feedback efficiency of the quasars can in principle be derived. The implied properties of the FeLoBALs are, however, surprising, with the thickness of the absorbers relative to their distance from the black hole, ΔR/R, as small as ∼10−5. Such absorbers are unlikely to survive the journey from the supermassive black hole to their inferred location. We show that the observed FeLoBAL properties are readily explained if they are formed in situ in radiative shocks produced when a quasar blast wave impacts a moderately dense interstellar clump along the line of sight. This physical picture differs significantly from the thin‐shell approximation often assumed, and implies outflow rates, kinetic luminosities and momentum fluxes that differ correspondingly, in some cases at the order‐of‐magnitude level. Using the radiative shock model, we estimate the ratio of the outflow kinetic luminosity to bolometric luminosity for three bright FeLoBAL quasars in the literature. We find per cent (and corresponding momentum fluxes ), similar to what is adopted in models reproducing the M–σ relation. These outflow properties are also comparable to those recently inferred for molecular outflows in local ultraluminous infrared galaxies, suggesting that active galactic nuclei are capable of driving such outflows.

UNSHIFTED METASTABLE He I* MINI-BROAD ABSORPTION LINE SYSTEM IN THE NARROW-LINE TYPE 1 QUASAR SDSS J080248.18+551328.9

“…If the absorber were produced in the immediate vicinity of the central SMBH, it would dissipate long before it arrives at the inferred location owing to Kelvin-Helmholtz instability. Therefore, the absorption gas of SDSS J0802+5513 should be generated in situ as that of the well-studied FeLoBAL quasars, the ionized gas of which is a consequence of radiative shocks from interaction of a quasar blast wave with dense interstellar clumps (Faucher-Giguère et al 2012). However, the FeLoBALs are typically blueshifted by several thousand kilometers per second with respect to the quasar systematic redshifts, unlike what we observed in SDSS J0802+5513.…”

THE DEPENDENCE OF C IV BROAD ABSORPTION LINE PROPERTIES ON ACCOMPANYING Si IV AND Al III ABSORPTION: RELATING QUASAR-WIND IONIZATION LEVELS, KINEMATICS, AND COLUMN DENSITIES

“…While other scenarios for BAL outflows also exist, such as those proposing that BALs primarily are formed at large distances (0.1-10 kpc) from the SMBH (e.g., Arav et al 2013; also see Faucher-Giguère et al 2012; but see Section 5.3 of Lucy et al 2014 for a critique), these have not been developed via numerical simulations to the point where robust comparisons with our observational find-ings are possible. Of course, any model for BAL winds, current or future, can be usefully constrained by our observational results presented above.…”

Powerful Outflows and Feedback from Active Galactic Nuclei

“…Here L i = l i L Edd is the ionizing luminosity, with l i < 1 a dimensionless parameter specified by the quasar spectrum, and N = ρ/µmp is the number density of the UFO gas. We use (22,25) …”