Hagai Netzer develops models connecting the spectral lines of active galactic nuclei to the conditions of their surrounding gas. In his account of emission-line physics, photons from the central source heat the gas by photoionization, while several atomic processes remove or redistribute that energy.
The resulting electron temperature follows a heating–cooling balance. It need not equal either the temperature assigned to the radiation field or the excitation temperature describing atomic level populations. This distinction is essential when interpreting a bright spectral line as a diagnostic of an illuminated cloud.[ref]
AGN Emission Lines by Hagai Netzer. Section 4.2, Thermal Equilibrium: kinetic, radiation and excitation temperatures; bound-free and collisional heating and cooling
Portrait of Hagai Netzer
. Via Wikimedia Commons; credits and usage information are on the linked source file page. Source.
New to topics? Read the docs here!