= Hagai Netzer
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<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.<AGN Emission Lines by Hagai Netzer>[Section 4.2, Thermal Equilibrium: kinetic, radiation and excitation temperatures; bound-free and collisional heating and cooling]{ref}
\Image[https://commons.wikimedia.org/wiki/Special:Redirect/file/Hagai_Netzer.jpg?width=260]
{title=Portrait of <Hagai Netzer>}
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{source=https://commons.wikimedia.org/wiki/File:Hagai_Netzer.jpg}
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