Annu. Rev. Astron. Astrophys. 2000. 38: 761-814 Copyright © 2000 by Annual Reviews. All rights reserved

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Abstract. More than a decade ago the IRAS satellite opened the realm of external galaxies for studies in the 10 to 100 µm band and discovered emission from tens of thousands of normal and active galaxies. With the 1995-1998 mission of the Infrared Space Observatory ¹, the next major steps in extragalactic infrared astronomy became possible: detailed imaging, spectroscopy, and spectrophotometry of many galaxies detected by IRAS, as well as deep surveys in the mid- and far-IR. The spectroscopic data reveal a wealth of detail about the nature of the energy source(s) and about the physical conditions in galaxies. ISO's surveys for the first time explore the infrared emission of distant, high-redshift galaxies. ISO's main theme in extragalactic astronomy is the role of star formation in the activity and evolution of galaxies.

Table of Contents

• INTRODUCTION: From IRAS to ISO
• NORMAL GALAXIES
• Infrared Emission from Normal Galaxies
• Mid-Infrared Emission: Unidentified Bands and Very Small Dust Grains
• Far-IR Emission: Cold Dust and Galactic Extinction
• Dark Matter in the Halos and Outer Parts of Disks
• Early-Type Galaxies
• ACTIVE GALAXIES
• Analytical Spectroscopy and Spectrophotometry
• Molecular Spectroscopy
• Distinguishing AGNs and Starbursts: ISO Diagnostic Diagrams
• Starburst Galaxies
• The Dark Side of Star Formation
• Properties and Evolution of Starbursts
• The [CII] Line as Global Tracer of Star Formation Activity in Galaxies
• Seyfert Galaxies and QSOs
• UIB Features in Seyfert Galaxies: Confirmation of Unified Models
• The Source of Far-Infrared Luminosity in Seyfert Galaxies and QSOs
• Re-constructing the Big Blue (EUV) Bump
• The Nature of Ultra-Luminous Infrared Galaxies
• Signature for AGN versus Starburst Activity: The ISO Diagnostic Diagram
• ULIRGs as a Class: The Starburst-AGN Connection
• Hidden AGNs: The Role of Dust Obscuration in ULIRGs
• Properties and Evolution of Star Formation in ULIRGs
• Warm ULIRGs and QSOs
• THE DISTANT UNIVERSE
• Mid-Infrared Surveys
• Source Counts: Evidence for Strong Evolution
• Nature of ISOCAM Sources: Luminous Star-Forming Galaxies at z ~ 0.7
• Far-Infrared Surveys
• Star Formation at High Redshift: A Synthesis
• CONCLUSIONS AND OUTLOOK
• REFERENCES

¹ The Infrared Space Observatory (ISO) is a project of the European Space Agency (ESA). The satellite and its instruments were funded by the ESA member states (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of the Japanese Space Agency ISAS and NASA. Back.