HI 21-cm absorption and unified schemes of active galactic nuclei

Preprint
Abstract
In this paper, we further explore the implications that this has for the currently popular consensus that it is the orientation of the torus, invoked by unified schemes of AGN, which determines whether absorption is present along our sight-line. The fact that at L1e23 W/Hz sources. These also give the apparently high 21-cm detection rate in compact objects, such as CSSs and GPSs. We find that ultra-violet luminosities can also explain why the presence of 21-cm absorption shows a preference for radio galaxies over quasars. From the profile widths and offsets from the systemic velocities, we find no discernible differences between the two AGN types. If the galactic disk shares a similar orientation to the central obscuration, this would suggest that the outflows of cold neutral gas, which would give rise to the absorption in type-1 AGN, have similar apparent kinematics to the toroidal gas. However, the fact that only half of the sources are detected in 21-cm, regardless of AGN type, may suggest that the bulk absorption generally occurs in the disk, which must therefore be randomly orientated with respect to the torus. Furthermore, we see no difference in the reddening between the two AGN types, indicating, like the 21-cm absorption, that the orientation of the torus has little bearing on this. It therefore appears that both the reddening and bulk HI are located in the disk, which is supported by the correlation between 21-cm line strength and the optical--near-infrared colour.