Radiative Transfer in the Broad Emission Line Regions of Quasistellar Objects
Abstract
Most of the photoionization models used to account for the broad emission lines from quasistellar objects have adopted escapeprobability approximations to avoid solving the equations of radiative transfer. The few published models based on transfer solutions have used the approximation of complete frequency redistribution for the hydrogen resonance lines. We show that both of these approximations lead to errors of at least factors of 2 in the calculated line ratios and to qualitative changes in the calculated atmospheric parameters. Here we solve the radiative transfer, statistical equilibrium, and energybalance equations for an illuminated, planeparallel cloud having a prescribed optical thickness and constant gas pressure. The cloud composition is assumed to be either pure hydrogen or H and He in the ratio 1 to 0.1. In addition, heavier elements are presumed to provide radiative cooling and heating and to absorb Xrays. Six energybalance models are presented, all having the same illuminating radiation, optical thickness, and pressure. The first is a pure hydrogen model considered earlier by Hubbard and Puetter. Model 2 includes the effects of radiative cooling by heavy elements. In model 3 we add helium and Xray opacity. Model 4 includes Xray heating. In model 5 we replace the "onthespot" approximation by a solution of the Lyman continuum transfer equation. In model 6, line escape probabilities are replaced by solutions of the line transfer equations, including Lyα partial frequency redistribution. The largest changes in the calculated results are due to heavyelement cooling and to the transfer effects with partial frequency redistribution.
 Publication:

The Astrophysical Journal
 Pub Date:
 August 1988
 DOI:
 10.1086/166550
 Bibcode:
 1988ApJ...331..211A
 Keywords:

 Emission Spectra;
 Galactic Nuclei;
 Line Spectra;
 Quasars;
 Radiative Transfer;
 Astronomical Models;
 Molecular Clouds;
 Astrophysics;
 GALAXIES: NUCLEI;
 QUASARS;
 RADIATION MECHANISMS;
 RADIATIVE TRANSFER