BAL and non-BAL quasars: continuum, emission, and absorption properties establish a common parent sample

Abstract

Using a sample of 144 000 quasars from the Sloan Digital Sky Survey data release 14 we investigate the outflow properties, evident both in absorption and emission, of high-ionization Broad Absorption Line (BAL) and non-BAL quasars with redshifts 1.6 z ≤ 3.5 and luminosities 45.3 < log 10 (L bol ) < 48.2 erg s −1 . Key to the investigation is a continuum and emission-line reconstruction scheme, based on meanfield independent component analysis, that allows the kinematic properties of the C ivλ1550 emission line to be compared directly for both non-BAL and BAL quasars. C iv-emission blueshift and equivalent-width (EW) measurements are thus available for both populations. Comparisons of the emission-line and BAL-trough properties reveal strong systematic correlations between the emission and absorption properties. The dependence of quantitative outflow indicators on physical properties such as quasar luminosity and luminosity relative to Eddington-luminosity are also shown to be essentially identical for the BAL and non-BAL populations. There is an absence of BALs in quasars with the hardest spectral energy distributions (SEDs), revealed by the presence of strong He iiλ1640 emission, large C ivλ1550-emission EW and no measurable blueshift. In the remainder of the C iv-emission blueshift versus EW space, BAL and non-BAL quasars are present at all locations; for every BAL-quasar it is possible to identify non-BAL quasars with the same emission-line outflow properties and SED-hardness. The co-location of BAL and non-BAL quasars as a function of emission-line outflow and physical properties is the key result of our investigation, demonstrating that (high-ionization) BALs and non-BALs represent different views of the same underlying quasar population.

Fe iii emission in quasars: evidence for a dense turbulent medium

“…The high-ionization C iv λ1549 emission line exhibits a large range of kinematic morphologies, from strong, 'peaky' emission at the systemic redshift which is believed to be dominated by emission from gas in virial equilibrium, to weaker and highly blueshifted emission tracing outflowing material. However, the physical mechanisms which set the balance of these emitting components are not well understood, despite the fact that the C iv morphology is known to be closely tied to other parameters such as the Eddington ratio and the hardness of the SED which is ionizing the BLR (Richards et al 2011;Rankine et al 2020). Here we note certain correlations using the results of the modelling of the λ1909 complex described in Section 5.…”

“…One possible explanation for the correlation between the strength of the Fe iii UV34 emission and the increasing blueshifted C iv emission, tracing outflowing lower density Figure 11. The equivalent width of Fe iii UV34 emission, shown against the observed blueshift of the C iv emission line (as defined in Rankine et al 2020), the Eddington ratio, and the equivalent width of He ii λ1640 emission. The strength of Fe iii increases with the signature of stronger nuclear outflows, which might be driven by higher L/L Edd .…”

“…The systemic redshifts used in this work are those described by Rankine et al (2020), which do not make use of the C iv line. This approach avoids biasing the systemic redshift estimation in cases where the C iv emission profile is skewed, which we have found to be an issue with the SDSS pipeline redshifts.…”

Exploring the link between C iv outflow kinematics and sublimation-temperature dust in quasars

“…Blue excesses can skew the location of the median line flux by up to ≈5000 km s −1 relative to the systemic redshift (Richards et al 2011). However, the C iv emission line is often contaminated by absorption features and so we calculate emission-line properties using the spectral reconstructions presented by Rankine et al (2020). Briefly, these reconstructions use the known correlation between the morphology of the 'C iii]' λ1909-emission complex and the blueshift of C iv to place priors on the weights of linear spectral components derived from a mean field independent component analysis of quasars which do not have any absorption features.…”

“…This increase in sample size allows the hot dust properties to be quantified in a much larger number of quasars, and for the dependence of these parameters on the emission line properties and the Eddington fraction to be explored simultaneously. Recent work by Rankine et al (2020) has developed an improved scheme for masking absorption features within the SDSS spectra, leading to an improved determination of the emission line properties in each object. In particular, the reported blueshift of the C iv emission line is now a more robust measurement of the strength of emission from outflowing gas.…”