Quasar emission lines as probes of orientation: implications for disc wind geometries and unification

Abstract

The incidence of broad absorption lines (BALs) in quasar samples is often interpreted in the context of a geometric unification model consisting of an accretion disc and an associated outflow. We use the the Sloan Digital Sky Survey (SDSS) quasar sample to test this model by examining the equivalent widths (EWs) of C iv 1550Å, Mg ii 2800Å, [O iii] 5007Å and C iii] 1909Å. We find that the emission line EW distributions in BAL and non-BAL quasars are remarkably similar -a property that is inconsistent with scenarios in which a BAL outflow rises equatorially from a geometrically thin, optically thick accretion disc. We construct simple models to predict the distributions from various geometries; these models confirm the above finding and disfavour equatorial geometries. We show that obscuration, line anisotropy and general relativistic effects on the disc continuum are unlikely to hide an EW inclination dependence. We carefully examine the radio and polarisation properties of BAL quasars. Both suggest that they are most likely viewed (on average) from intermediate inclinations, between type 1 and type 2 AGN. We also find that the low-ionization BAL quasars in our sample are not confined to one region of 'Eigenvector I' parameter space. Overall, our work leads to one of the following conclusions, or some combination thereof: (i) the continuum does not emit like a geometrically thin, optically thick disc; (ii) BAL quasars are viewed from similar angles to non-BAL quasars, i.e. low inclinations; (iii) geometric unification does not explain the fraction of BALs in quasar samples.

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

“…11 are extremely similar across the whole wavelength range. The composite spectra themselves are also very similar, apart from the presence of troughs in the BAL spectra, in agreement with Weymann et al (1991) and Matthews et al (2017). There are, however, subtle differences in some of the emission lines at certain areas in C iv-emission space which can only be seen when dividing the BAL spectra (reconstructions) by the non-BAL spectra (reconstructions) as shown in the bottom panel.…”

Physical Properties of 15 Quasars at z ≳ 6.5

“…The velocity can be estimated from the width of the emission line: v f FWHM, 10 BLR =´( ) with f a geometrical factor accounting for projection effects (e.g., Decarli et al 2008;Grier et al 2013;Matthews et al 2017).…”

Monte Carlo radiative transfer

“…Abbott and Lucy 1985;Lucy and Abbott 1993;Schaerer and Schmutz 1994;Schmutz 1997;Vink et al 1999Vink et al , 2000Sim 2004;Müller and Vink 2008;Muijres et al 2012b;Lucy 2012b;Noebauer and Sim 2015;Vink 2018), to determine synthetic light curves and spectra for SNe (see e.g. Mazzali and Lucy 1993;Lucy 1999a;Mazzali 2000;Lucy 2005;Kasen et al 2006;Sim 2007;Kromer and Sim 2009;Wollaeger et al 2013;Wollaeger and van Rossum 2014;Kerzendorf and Sim 2014;Bulla et al 2015;Magee et al 2018) or to treat RT in winds emanating from accretion discs of cataclysmic variables (Knigge et al 1995;Long and Knigge 2002;Noebauer et al 2010;Kusterer et al 2014;Matthews et al 2015) or active galactic nuclei (Sim 2005;Sim et al 2010Sim et al , 2012Higginbottom et al 2013;Matthews et al 2016Matthews et al , 2017Tomaru et al 2018). In applications such as these, our current implicit assumption, namely that RT occurs in static media or in environments with material velocities low enough to be safely ignored, can no longer be maintained.…”

“…Lucy 1983;Abbott and Lucy 1985;Lucy and Perinotto 1987;Hillier 1991;Lucy and Abbott 1993;Schmutz 1997;Vink et al 1999;Harries 2000;Vink et al 2000;Sim 2004;Watanabe et al 2006;Lucy 2007;Müller and Vink 2008;Lucy 2010;Vink et al 2011;Lucy 2012a,b;Muijres et al 2012a,b;Šurlan et al 2012Müller and Vink 2014;Lucy 2015;Noebauer and Sim 2015;Vink 2018), mass outflows from disks (e.g. Knigge et al 1995;Knigge and Drew 1997;Long and Knigge 2002;Sim 2005;Sim et al 2005Sim et al , 2008Noebauer et al 2010;Sim et al 2010;Odaka et al 2011;Sim et al 2012;Higginbottom et al 2013;Kusterer et al 2014;Hagino et al 2015;Matthews et al 2015Matthews et al , 2016Matthews et al , 2017Tomaru et al 2018), or supernovae (e.g. Lucy 1987;Janka and Hillebrandt 1989;Mazzali and Lucy 1993;Lucy 1999b;…”