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Article Contents

ABSTRACT

1.INTRODUCTION

2. OBSERVED PROPERTIES AND EMPIRICAL CLASSIFICATION OF AGN

3.ANISOTROPIC RADIATION FROM OBSCURATION

3.1. Polarimetric Evidence for Hidden Nuclear Regions

3.2. Infrared and X-Ray Evidence for Hidden Nuclear Regions

3.3. Anisotropic Illumination of Narrow Emission Line Gas

4. ANISOTROPIC RADIATION FROM RELATIVISTIC BEAMING

4.1. Evidence for Relativistically Beamed Gamma-Rays

4.2. Superluminal Motion in Radio Jets

4.3. Observed Radio Jet Asymmetries

4.4. Brightness Temperature Calculations and SSC Models

5. BASIS FOR UNIFICATION SCHEMES

5.1. History of Radio-Loud Unification Schemes

5.2. Distinction between FR I and FR II Radio Galaxies

5.3. Isotropic Properties of Quasars and FR II Galaxies

5.3.1. Extended Radio Emission

5.3.2. Narrow Emission Lines

5.3.3. Infrared Properties

5.3.4. Host Galaxies

5.3.5. Environments

5.3.6. Cosmic Evolution

5.4 Isotropic Properties of BL Lac Objects and FR I Galaxies

5.4.1. Extended Radio Emission

5.4.2. Narrow Emission Lines

5.4.3. Host Galaxies

5.4.4. Environments

5.5. The Myth of Unbiased Selection

5.6. Effect of Relativistic Beaming on Number Statistics

6. STATISTICAL UNIFICATION OF RADIO-LOUD AGN

6.1. Unification of Radio Quasars and FR II Galaxies

6.1.1. Content of the 2 Jy Sample of Radio Sources

6.1.2. Observed LFs of High-Luminosity Radio Sources

6.1.3. Beamed LFs of High-Luminosity Radio Sources

6.2. Unification of BL Lac Objects and FR I Galaxies

6.2.1. X-Ray and Radio Samples of BL Lac Objects

6.2.2. Properties of X-Ray-Selected and Radio-Selected BL Lac Objects

6.2.3. Population Statistics for X-Ray Samples

6.2.4. Population Statistics for Radio Samples

6.2.5. Relation of X-Ray- and Radio-Selected BL Lac Objects

6.2.6. New Terminology and a New Connection Between BL Lac Classes

6.3. Independent Estimates of Relativistic Beaming Parameters

7. RELATION OF QUASARS AND BL LAC OBJECTS

7.1. Low- and High-Redshift BL Lac Objects

7.2. Possible Connections between BL Lac Objects and FSRQ

7.2.1. The Evolutionary Connection

7.2.2. Multiwavelength Spectral Continuity of BL Lac Objects and FSRQ

7.2.3. BL Lac Objects as Gravitationally Micro-Lensed FSRQ

8. THE VIABILITY OF UNIFIED SCHEMES

8.1. Potential Problems with Unification

8.1.1. Linear Sizes of Blazars and Radio Galaxies

8.1.2. Dependence of Quasar Fraction on Redshift

8.1.3. Absence of Superluminal Motion in Radio Galaxies

8.1.4. The Parent Population of BL Lac Objects

8.2. Possible Complications for Unification

8.2.1. Properties of the Obscuring Torus

8.2.2. Cosmic Evolution of Radio-Loud AGN

8.2.3. Parameterization of Relativistic Beaming

8.2.4. Compact Steep-Spectrum and Gigahertz Peaked-Spectrum Sources

8.2.5. Selection Effects in the Identification of Quasars

8.2.6. Extended Continuum Emission in Type 2 AGN

9. THE TEN MOST IMPORTANT QUESTIONS

A. RELATIVISTIC BEAMING PARAMETERS

B. DOPPLER ENHANCEMENT

C. RATIO OF CORE- TO EXTENDED-FLUX

D. GLOSSARY OF ACRONYMS

REFERENCES