9. ACTIVE GALACTIC NUCLEI

9.1 Taxonomy

• Radio galaxies
  
• Quasars and BL Lac objects
  
• Seyfert 1 galaxies
  
• Seyfert 2 galaxies
  
• LINERs
  
  

9.2 Demographics

• Number densities compared to galaxy densities
  
• Evidence for evolution
  
• Peak in quasar densities at .
  
  

9.3 Emission-Line Physics

• Hydrogen spectrum
  
• Forbidden lines
  
• Models of the broad-and narrow-line regions
  
  

9.4 Continuum Radiation

• Thermal components; dust scattering
  
• Nonthermal radiation: synchrotron radiation
  
• Jets: properties; relativistic beaming
  
• Gamma rays
  

9.5 The Unified Model of Nuclear Activity in Galaxies

9.6 Power Sources

• Starbursts: pro and con
  
• Black holes: pro and con
  
• The critical observations that imply black hole engines
  
• The Galactic center