Radio-loud AGN See main article radio galaxies for discussion of the large-scale behaviour of the jets. Here only the active nuclei are discussed. • Radio-loud quasars. These behave exactly like radio-quiet quasars with the addition of emission from a jet. Thus they show strong optical continuum emission, broad and narrow emission lines, and strong X-ray emission, together with nuclear and often extended radio emission. • ' Blazars ' ( BL Lac objects and OVV quasars ). These classes are distinguished by rapidly variable, polarized optical, radio and X-ray emission. BL Lac objects show no optical emission lines, broad or narrow, so that their redshifts can only be determined from features in the spectra of their host galaxies. The emission-line features may be intrinsically absent or simply swamped by the additional variable component: in the latter case, emission lines may become visible when the variable component is at a low level. 
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.