Radiation pressure confinement - I. Ionized gas in the ISM of AGN hosts

Jonathan Stern, Ari Laor, Alexei Baskin

Research output: Contribution to journalArticlepeer-review


We analyse the hydrostatic effect of active galactic nucleus (AGN) radiation pressure on optically thick gas in the host galaxy. We show that in luminous AGN, the radiation pressure likely confines the ionized layer of the illuminated gas. Radiation pressure confinement (RPC) has two main implications. First, the gas density near the ionization front is 7 × 104Li,45r-250 cm-3, where Li, 45 is the ionizing luminosity in units of 1045 erg s-1 and r50 is the distance of the gas from the nucleus in units of 50 pc. Secondly, as shown by Dopita et al., the solution of the ionization structure within each slab is unique, independent of the ambient pressure.We show that the RPC density versus distance relation is observed over a dynamical range of ~104 in distance, from sub-pc to kpc from the nucleus, and a range of ~108 in gas density, from 103 to 1011 cm-3. This relation implies that the radiative force of luminous AGN can compress giant molecular clouds in the host galaxy and possibly affect the star formation rate. The unique ionization structure in RPC includes a highly ionized X-ray-emitting surface, an intermediate layer which emits coronal lines and a lower ionization inner layer which emits optical lines. This structure can explain the observed overlap of the extended X-ray and optical narrow line emission in nearby AGN. We further support RPC by comparing the predicted ratios of the narrow line strength and narrow line widths with available observations. We suggest a new method, based on the narrow line widths, to estimate the black hole mass of low-luminosity AGN.

Original languageEnglish
Pages (from-to)901-921
Number of pages21
Issue number2
StatePublished - Mar 2014


  • General
  • Radiation mechanisms

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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