Radiation pressure and absorption in AGN: results from a complete
  unbiased sample from Swift
  Outward radiation pressure can exceed the inward gravitational pull on gas
clouds in the neighbourhood of a luminous Active Galactic Nucleus (AGN). This
creates a forbidden region for long-lived dusty clouds in the observed columnn
density - Eddington fraction plane. (The Eddington fraction lambda_Edd is the
ratio of the bolometric luminosity of an AGN to the Eddington limit for its
black hole mass.) The Swift/BAT catalogue is the most complete hard X-ray
selected sample of AGN and has 97 low redshift AGN with measured column
densities N_H and inferred black hole masses. Eddington fractions for the
sources have been obtained using recent bolometric corrections and the sources
have been plotted on the N_H - lambda_Edd plane. Only one source lies in the
forbidden region and it has a large value of N_H due to an ionized warm
absorber, for which radiation pressure is reduced. The effective Eddington
limit for the source population indicates that the high column density clouds
in the more luminous objects lie within the inner few pc, where the central
black hole provides at least half the mass. Our result shows that radiation
pressure does affect the presence of gas clouds in the inner galaxy bulge. We
discuss briefly how the N_H - lambda_Edd plane may evolve to higher redshift,
when feedback due to radiation pressure may have been strong.
