On the orbital motion of Broad-Line Region clouds
I talk about orbital motion of spherical, pressure-confined clouds in the broad-line region (BLR) of active galactic nuclei (AGNs). Not only the gravity of the central object and the force to the radiation pressure are considered, but the effect of a drag force are investigated. We showed that when the background pressure profile depends on the radial distance and the latitudinal angle, the stability considerations imply that BLR clouds tend to populate the equatorial regions more than other parts. It seems that this finding is valid so long as the pressure distribution of the intercloud medium decreases from the equator to the pole. I then extend the present model by considering a drag force in proportion to the velocity square. I then discuss that the clouds will generally fall onto the central object very quickly which implies that some mechanisms for continuous creation of the clouds should operate in these systems.