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Article Contents

ABSTRACT

1.HISTORICAL INTRODUCTION

2.OPTICAL SPECTRA

2.1.Classification

2.2.Diagnostics

2.3.Photoionization

2.4.Broad-line region

2.5.Accretion disk continuum

2.6.Ultraviolet line spectra

2.7.Temporal variation

2.8.Completeness of Seyfert galaxy samples

3.OTHER WAVELENGTH REGIONS

3.1.Radio-frequency spectral region

3.2.Infrared continuum

3.3.X-ray region

3.4.Gamma-ray radiation

4.TORUS MODEL

4.1.Cylindrical symmetry

4.2.Seyfert 2s with `hidden' BLRs

4.3.Ionization cones

5.VELOCITY FIELDS

5.1.Narrow-line profiles

5.2.Extended emission-line region

5.3.Overall NLR velocity field

5.4.BLR velocity field

5.5.Possible magnetic fields

6.CONTINUITY OF AGN PROPERTIES

6.1.QSOs and Seyfert 1 galaxies

6.2.Quasars and radio galaxies

6.3.Few high-luminosity Seyfert 2s

6.4.LINERs

7.FUELLING

7.1.Introduction

7.2.Luminosity functions of AGNs

7.3.Black holes in normal galaxies

7.4.Clusters, groups and neighbor galaxies

7.5.Interactions and mergers

8.EVOLUTION

8.1.Fuelling black holes

8.2.Formation rate

8.3.QSOs in formation

9.MISCELLANEOUS

9.1.Molecular gas

9.2.Warmers

10.CONCLUSION

REFERENCES