Taxonomy of AGN - circa 1980 Seyfert 1 galaxy Seyfert 2 galaxy QSO Broad Absorption Line (BAL) QSO Liner Quasar Fanaroff/Riley FR1 and FR2 galaxy Broad line radio galaxy Narrow line radio galaxy Flat Spectrum Core Dominant Radio Source Steep Spectrum Lobe Dominant Radio Source BL Lac object Optically Violent Variable Quasar “Radio-quiet” “Radio-loud”

Two Basic Resources on Unification Antonucci, R.R.J. 1993, ARAA, 31, 473 – Unification models for AGN & Quasars Urry & Padovani 1995, PASP, 107, 803 – Radio loud objects only

Spectral “Types” of Emission-Line AGN Ha Hg Hb [O III] 4959,5007 Type 1

Ancient History (Rowan-Robinson 1977)

Early Evidence for Aspect-dependent Classification Alignment of optical polarization PA with radio structure in Type 1 objects (polarization typically <1%). Anti-alignment of optical polarization PA with radio structure in Type 2 objects (polarization 1-5+%). General alignment of “ionization cones” with radio structure.

Radio Structure vs. Optical Polarization (Antonucci 1983)

The Hidden Seyfert 1 Nucleus in NGC 1068 (Antonucci & Miller 1985) Polarized flux 7500 km/sec Total flux 8 minutes of data in 1998 vs. 20 hrs in 1984!

The Hidden Seyfert 1 Nucleus in NGC 1068 (Antonucci & Miller 1985) Dusty, molecular torus

A Slightly More Modern Picture tv ~ 0.01? R ~few kpc tv ~ 100 R ~ 100-500 pc

How the Torus Unifies AGN Classifications Type 1 Type 1.5 Torus axis does not align with the axis of the galaxy! Type 1 in polarized light NLR BLR Type 2 Dust grains

Polarization at High Inclination (Type 2) Strong polarization Perpendicular to torus axis

Polarization at Low Inclination (Type 1) Weak polarization Parallel to torus axis

Clinching Evidence: Direct imaging of Torus (Ford et al. 1997)

Clinching Evidence: Images of Ionization Cones (e. g. , Zakamska et al

The LINER Galaxy NGC 4258 N E D = 7 Mpc

H20 Maser Emission from NGC 4258 (Miyoshi, Cecil et al. 1992-95) From Keplerian velocities of masers, central (black hole) mass is 3.6x107 M¤ v µ r -1/2 Keplerian velocity curves

Polarized Emission Lines from NGC 4258 (Wilkes et al. 1995) Dv = 1000 km/s P.A. = 86o

Red and Polarized QSOs from 2MASS (Smith et al. 2000)

A Type 2, Red QSO Comes out of the Closet (Schmidt et al. 2002) Dv = 30,000 km/s!

What is Wrong with these QSOs? (Smith et al. 2003)

Red Type1 QSOs are Polarized! Type 1 objects (All show broad lines)

Hypothesis for Reddened, Polarized Type 1 QSOs Reddening/scattering by considerable dust, even in polar directions Hypothesis for Reddened, Polarized Type 1 QSOs NLR BLR Dust grains

Increased Scattering will Cause Reddest QSOs to Appear as Type 1 Regardless of Orientation Deficit of [O III] Surplus of [O III]

Unification of Radio-Quiet AGN Liner? Seyfert 1 galaxy Seyfert 2 galaxy Type 1 QSO BAL QSO? Type 2 QSO “Face-on” “Edge-on” Luminosity

Unification of Radio-Loud AGN BL Lac object = Optically Violent Variable Quasar “Face-on” Broad line radio galaxy FR1, FR2, Narrow line radio galaxy Flat Spectrum Core Dominant Radio Source Steep Spectrum Lobe Dominant Radio Source Quasar “Edge-on” Luminosity