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Tom Esposito Astr 278 2012 Feb 09
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Seyfert 1, Seyfert 2, QSO, QSO2, LINER, FR I, FR II, Quasars, Blazars, NLXG, BALQ…
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1. All AGN are intrinsically the same and we are just viewing them differently OR 2. Each type of AGN is a distinct phenomenon OR 3. Some combination of 1 and 2
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Radio-quiet Seyfert 1 Seyfert 2 QSO QSO2 LINERs? Radio-loud FR I, FR II Quasars Blazars Unified Model
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All radio-quiet AGN have the same central engine Credit: C. M. Urry and P. Padovani Supermassive black hole + hot accretion disk at center
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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
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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
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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
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Narrow emission 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
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Seyfert 2 Seyfert 1
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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
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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
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Molecular gas in torus with 10 24 cm -2 < N H < 10 25 cm -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
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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???
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Chris Reynolds
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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?
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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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Obscuring torus blocks broad lines in Type 2’s 1-several pc (based on x-rays) (or 100+?? Based on IR) scale radially, 0.1-1 pc vertically Inner edge defined by dust sublimation temp N H > 10 24 cm -2 Type 2 continuum is also weaker than Type 1 Warm electrons scatter and polarize featureless continuum light from nuclear region in Type 2’s Matches Type 1’s except polarized Antonucci & Miller 1995 spectropolarimetry
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Torus dust absorbs optical broad lines along direct line of sight to observer Often assumed coaxial with BH spin axis – ang momentum conservation Line emission aimed out of torus plane gets scattered towards observer in polarized light Near-IR broad line emission passes through torus more easily than optical Torus is only geometrically wide enough to obscure broad line region and not narrow line region High equivalent width Fe K-α line observed in Type 2’s – direct x-ray photons absorbed by Compton thick medium; observed weak continuum and iron line is reflected off that medium Narrow line region should have bi-conical shape based on opening angle of torus – observed with high-resolution HST imaging (Pogge 1998, Barbosa et al. 2009) Axis of cones often slightly misaligned with minor axis of host galaxy and radio jets – torus and central engine misaligned
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Torus often modeled as smooth mix of gas and dust – difficulty in keeping torus geometrically thick (puffy) Idea of thin disk tilted or warped Models recently of clumpy medium ▪ Supported by recent x-ray observations, as Robin will discuss ▪ Also by broad IR SED – needs either huge torus (100 pc; not observed) or clumpy medium ▪ Nenkova et al. 2002, 2008 mostly successful in reproducing mid-IR observations with clumps (if smooth, dust would be destroyed too quickly by hot surrounding gas, Krolik & Begelman 1988)
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