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AGN: The Unified Model

AGN: The Unified Model. Tom Esposito Astr 278 2012 Feb 09. Many different types of AGN have been observed. Seyfert 1, Seyfert 2, QSO, QSO2, LINER, FR I, FR II, Quasars, Blazars , NLXG, BALQ…. How can we explain this variety?.

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AGN: The Unified Model

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  1. AGN: The Unified Model Tom Esposito Astr 278 2012 Feb 09

  2. Many different types of AGN have been observed Seyfert1, Seyfert 2, QSO, QSO2, LINER, FR I, FR II, Quasars, Blazars, NLXG, BALQ…

  3. How can we explain this variety? • All AGN are intrinsically the same and we are just viewing them differently OR • Each type of AGN is a distinct phenomenon OR • Some combination of 1 and 2 Unified Model

  4. “Unified” Model consists of 2 schemes – radio-quiet & radio-loud Unified Model Radio-quiet • Seyfert 1 • Seyfert 2 • QSO • QSO2 • LINERs? Radio-loud • FR I, FR II • Quasars • Blazars

  5. All radio-quiet AGN have the same central engine Supermassive black hole + hot accretion disk at center SMBH Accretion Disk Credit: C. M. Urry and P. Padovani

  6. BLR gas excited by UV photons emits broad optical lines Supermassive black hole + hot accretion disk at center Hot, high velocity, dense gas clouds near BH form broad-line region

  7. Dust & gas torus may obscure central regions of AGN Supermassive black hole + hot accretion disk at center Hot, high velocity, dense gas clouds near BH form broad-line region Compton-thick dusty torus surrounds engine and broad-line region

  8. Hot electrons outside torus and BLR scatter nuclear emission Supermassive black hole + hot accretion disk at center Hot, high velocity, dense gas clouds near BH form broad-line region Compton-thick dusty torus surrounds engine and broad-line region Hot electrons scatter polarized continuum + broad-line emission

  9. Narrowemission lines from gas within ionization cones Supermassive black hole + hot accretion disk at center Hot, high velocity, dense gas clouds near BH form broad-line region Compton-thick dusty torus surrounds engine and broad-line region Hot electrons scatter polarized continuum + broad-line emission Cool, low velocity, low density gas clouds beyond torus edge form narrow-line region

  10. Orientationis the onlyfactor that determines if we see aType 1 or Type 2 AGN! Seyfert 2 Seyfert 1

  11. All AGN are intrinsically Type 1 • Featureless optical/UV continuum, soft and hard x-rays from nucleus • Broad permitted optical emission lines • Narrow permitted and forbidden emission lines • IR emission from dust reprocessing of nuclear light

  12. Direct imaging of disk-shaped dust around suspected AGN

  13. Direct imaging of disk-shaped dust around suspected AGN

  14. Spectropolarimetry suggests that Type 2 AGN are obscured Type 1’s • NGC 1068 shows Type 2 spectrum overall but Type 1 spectrum in polarized light (Antonucci & Miller 1985) • Electrons polarize and scatter nuclear emission and broad emission lines into observer’s line-of-sight. O

  15. 2-10 keV x-ray flux is reduced in Type 2 AGN by torus absorption • Molecular gas in torus with 1024 cm-2 < NH < 1025cm-2 absorbs only low energy x-rays • Short-period variability of x-ray absorption implies torus inner edge < 1 pc from nucleus and no more than 10 pc in radial extent (Risaliti et al. 1999, 2002, 2005) • Fe K-α line reflection requires a mirror

  16. Other observational evidence is less substantial • Lack of QSO2’s matches prediction of large torus opening angle at high luminosities • Requires AGN to have different-sized tori, which is a modification of the standard unified model • Clumpy torus models can explain mid-IR SED’s of Type 2 AGN • But is a clumpy torus still the Unified Model???

  17. Radio-loud unification similar to radio-quiet but with radio emission Chris Reynolds

  18. Evidence against the Unified Model or not? • Recent efforts to reproduce mid-IR observations of Type-1 and Type-2 Seyferts by Almeida et al. 2011 used clumpy torus models • They found more dependence on torus morphology than inclination • Type-2’s have broader, clumpier, more opaque tori • Does this matter much to the Unified Model?

  19. Summary • Unified Model asserts that differences between Type 1 and Type 2 AGN are due to viewing angle only! • Optical/UV, IR, and x-ray observations support this model to a degree • Radio-loud AGN are unified with similar scheme to radio-quiet but with less certainty

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