Broad-line active galactic nuclei rotate faster than narrow-line ones

Abstract

The super-massive black holes of 10(6)M(⊙) to 10(9)M(⊙) that reside in the nuclei of active galaxies (AGN) are surrounded by a region emitting broad lines, probably associated with an accretion disk. The diameters of the broad-line regions range from a few light-days to more than a hundred light-days, and cannot be resolved spatially. The relative significance of inflow, outflow, rotational or turbulent motions in the broad-line regions as well as their structure (spherical, thin or thick accretion disk) are unknown despite intensive studies over more than thirty years. Here we report a fundamental relation between the observed emission linewidth full-width at half-maximum (FWHM) and the emission line shape FWHM/σ(line) in AGN spectra. From this relation we infer that the predominant motion in the broad-line regions is Keplerian rotation in combination with turbulence. The geometry of the inner region varies systematically with the rotation velocity: it is flattest for the fast-rotating broad-line objects, whereas slow-rotating narrow-line AGN have a more spherical structure. Superimposed is the trend that the line-emitting region becomes geometrically thicker towards the centre within individual galaxies. Knowing the rotational velocities, we can derive the central black-hole masses more accurately; they are two to ten times smaller than has been estimated previously.

Orientation effects on spectral emission features of quasars

“…In the same BLR disk-shaped scenario it has also been suggested that the kinematics of this inner region, consisting of a combination of rotational and turbulent motions, could affect its geometry, with broader lines emitted from more flattened regions (Kollatschny & Zetzl 2011). Moreover, the proximity of the BLR to the obscuring "torus" of the Unified Model (Antonucci 1993) suggests a smooth connection between the two structures, rather than two completely separated regions, as usually described in the standard unification model.…”

Low- and High-zHighly Accreting Quasars in the 4D Eigenvector 1 Context

“…A flattened geometry of the line emitting region [136,74,22,46] is suggested by the dependence of line width on the viewing angle. There are few fortunate cases when the viewing angle can be estimated (for example, if superluminal motion is detected: [119]); otherwise, orientation effects emerge on a statistical basis by comparing the average line widths of LD and CD RL sources [72,140].…”

Modelling photometric reverberation data: a disk-like broad-line region and a potentially larger black hole mass for 3C 120

“…Although there is no clear consensus about the geometry of the BLR, past studies have shown evidence in favour of a disk-like configuration (e.g., Wills & Browne 1986;Murray & Chiang 1997;Bottorff et al 1997;Elvis 2000;Konigl & Kartje 1994;Kollatschny 2003a,b;Kollatschny & Zetzl 2011, 2013. Kollatschny & Zetzl (2011, 2013 analysed the shape of the rms line profiles of a homogenous AGN subsample of Peterson et al (2004) and found evidence for the superposition of rotational disk-like components and turbulence.…”