Tidally disrupted dusty clumps as the origin of broad emission lines in
  active galactic nuclei
  Type 1 active galactic nuclei display broad emission lines, regarded as
arising from photoionized gas moving in the gravitational potential of a
supermassive black hole. The origin of this broad-line region gas is unresolved
so far, however. Another component is the dusty torus beyond the broad-line
region, likely an assembly of discrete clumps that can hide the region from
some viewing angles and make them observationally appear as Type 2 objects.
Here we report that these clumps moving within the dust sublimation radius,
like the molecular cloud G2 discovered in the Galactic center, will be tidally
disrupted by the hole, resulting in some gas becoming bound at smaller radii
while other gas is ejected and returns to the torus. The clumps fulfill
necessary conditions to be photoionized. Specific dynamical components of
tidally disrupted clumps include spiral-in gas as inflow, circularized gas, and
ejecta as outflow. We calculate various profiles of emission lines from these
clouds, and find they generally agree with H$\beta$ profiles of Palomar-Green
quasars. We find that asymmetry, shape and shift of the profiles strongly
depend on [O III], luminosity, which we interpret as a proxy of dusty torus
angles. Tidally disrupted clumps from the torus may represent the source of the
broad-line region gas.
