Theoretical Quasar Emission Line Ratios - Part Two - Hydrogen Lyman-Alpha Balmer and Paschen Lines and the Balmer Continuum

Details Theoretical Quasar Emission Line Ratios - Part Two - Hydrogen Lyman-Alpha Balmer and Paschen Lines and the Balmer Continuum Theoretical Quasar Emission Line Ratios - Part Two - Hydrogen Lyman-Alpha Balmer and Paschen Lines and the Balmer Continuum

Jan 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981apj...243..390c&link_type=abstract

Astrophysical Journal, Vol.243, P. 390, 1981

Mathematics

Probability

64

Scientific paper

We explore the formation of the hydrogen La, Balmer, and Paschen lines and the Balmer continuum in highly idealized QSO broad emission line clouds (ELCs) of constant temperature and density irradiated by an external source of power-law spectral form. We simultaneously solve the equations governing excitation, ionization, and transfer of both external and diffuse radiation fields. Our calculations show that the typical observed broad emission line ratios of Lα/Hα, Hβ/Hα, Pα/Hα, and Balmer continuum/Hα can be understood for ELC conditions in the temperature range 7 × 103 ≲ Te ≲ 2 × 104 K, hydrogen density range 108 ≲ nH ≲ 1012 cm-3, and for external fluxes F ≲-6 ergs cm-2 s-1 Hz-1 at the Lyman continuum limit.
Important results are:
1. The Lα/Hα ratio is very sensitive to the optical thickness of the cloud at the optical thickness that we think are appropriate for QSOs.
2. It is not necessary to postulate dust either internal or external to the ELC.
3. The ELCs are very optically thick; the Balmer lines and Pa originate in a region for which the Lyman-limit optical depth τcl ≳ 102.
4. A very extended ionized zone results from ionization from excited states.
5. The radiation from various transitions arises from very extended and sometimes quite different regions of the cloud. This renders a mean escape probability approach inappropriate.
6. Predicted line ratios and cooling rates depend critically on the functional form of the photon escape probability.
7. Acceptable values of the area covering factor and static energy balance require temperatures somewhat in excess of 104 K.

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