Radiative acceleration of coronal gas in Seyfert nuclei

The line ratios from coronal gas in Seyferts can be successfully fitted with photoionized clouds of high densities and low volume filling factor. The ionization parameter implied is sufficiently high that models must consider the effect of radiation pressure from the active nucleus. In spite of the gravitational force of the nucleus, radiation pressure is sufficiently strong to compress and radially accelerate the internally stratified gas clouds provided that these contain small amounts of dust (~=10 per cent of the solar neighbourhood value). This radial acceleration could explain the blueshift of the coronal lines relative to the systemic velocity without the need to invoke an ambient `pushing' wind. Embedded dust has the interesting effect of making the photoionized clouds marginally ionization-bounded instead of matter-bounded.