|Annu. Rev. Astron. Astrophys. 1996. 34:
Copyright © 1996 by Annual Reviews Inc. All rights reserved
One of the most important discoveries from extragalactic observations at mid- and far-infrared wavelengths has been the identification of a class of ``infrared galaxies'', objects that emit more energy in the infrared (~ 5-500µm) than at all other wavelengths combined. The first all-sky survey at far-infrared wavelengths carried out in 1983 by the Infrared Astronomical Satellite (IRAS) resulted in the detection of tens of thousands of galaxies, the vast majority of which were too faint to have been included in previous optical catalogs. It is now clear that part of the reason for the large number of detections is the fact that the majority of the most luminous galaxies in the Universe emit the bulk of their energy in the far-infrared. Previous assumptions, based primarily on optical observations, about the relative distributions of different types of luminous galaxies - e.g. starbursts, Seyferts, and quasi-stellar objects (QSOs) - need to be revised.
The bulk of the luminosity produced in galaxies bolometrically more luminous than ~ 4 L* (i.e. Lbol 1011 L) appears to be produced in objects that are heavily obscured by dust. Although luminous infrared galaxies (hearafter LIGs: Lir >1011 L) are relatively rare objects, reasonable assumptions about the lifetime of the infrared phase suggest that a substantial fraction of all galaxies with LB > 1010 L pass through such a stage of intense infrared emission (Soifer et al. 1987b).
Substantial progress has been made in cataloging infrared galaxies detected in the IRAS database, allowing for a good determination of the luminosity function over a wide range of infrared luminosity (Lir ~ 107-1013 L). A brief review of IRAS galaxy redshift surveys and a comparison of the infrared galaxy luminosity function with other classes of extragalactic objects is given in Section 3. Section 4 reviews published multiwavelength data for complete samples of the brightest infrared sources and selected samples of the most luminous infrared objects. Section 5 discusses the origin and evolution of LIGs and presents detailed data for several well-studied objects. Several important phenomena associated with LIGs that may significantly impact other areas of extragalactic research are reviewed in Section 6, and Section 7 briefly discusses how theoretical simulations are being used to more accurately interpret the observed morphology and kinematics of both the gas and dust in LIGs.
This review is the first to focus almost exclusively on the properties of luminous infrared galaxies. Pre-IRAS reviews of extragalactic infrared observations by Neugebauer et al. (1971) and Rieke & Lebofsky (1979) include discussions of luminous infrared emission from optically selected objects. Soifer et al. (1987a) present a broad overview of the extragalactic sky as seen by IRAS, including a detailed discussion of the infrared galaxy luminosity function and some discussion of the properties of a few selected LIGs, while the review by Telesco (1988) provides an excellent complimentary summary focusing on the properties of nearby, lower luminosity infrared galaxies. Recent reviews by Young & Scoville (1991) on the molecular gas properties of galaxies and by Barnes & Hernquist (1992) on theoretical models of interacting galaxies cover topics that are particularly relevant to the study of LIGs.