2001/04/16 by Doron Chelouche, D. Chelouche, Hagai Netzer +1 · 4 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #astro-ph
paper · pdf · doi:10.1046/j.1365-8711.2001.04586.x
published as Mon.Not.Roy.Astron.Soc. 326 (2001) 916 · 10 pages, 10 figures, LaTex mn.sty, Accepted for publication by the MNRAS
arxiv created 2001/04/16 · openalex publication_date 2001/09/21 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We present calculations of the dynamics of highly ionized gas (HIG) clouds that are confined by external pressure, and are photoionized by AGN continuum. We focus on the gas that is seen, in absorption, in the X-ray spectrum of many AGN and show that such gas can reach hydrostatic equilibrium under various conditions. The principal conclusion is that the clouds can be accelerated to high velocities by the central X-ray source. The dynamical problem can be reduced to the calculation of a single parameter, the average force multiplier, 〈M〉. The typical value of 〈M〉 is ∼10 suggesting that radiation pressure acceleration by X-rays is efficient for L/LEdd≳0.1. The terminal velocity scales with the escape velocity at the base of the flow and can exceed it by a large factor. The typical velocity for a HIG flow that originates at R=1017cm in a source with Lx=1044erg s−1 is ∼1000 km s−1, i.e. similar to the velocities observed in several X-ray and UV absorption systems. Highly ionized AGN clouds are driven mainly by bound–free absorption, and bound–bound processes are less important unless the lines are significantly broadened or the column density is very small. Pressure laws that result in constant or outward decreasing ionization parameters are most effective in accelerating the flow.