High-Energy Astrophysics American and Soviet Perspectives/Proceedings from the U.S.-U.S.S.R. Workshop on High-Energy Astrophysics (1991) / Chapter Skim
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ULTRALUMINOUS INFRARED GALAXIES
ULTRALUMINOUS INFRARED GALAXIES
Pages 344-355
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From page 344... ...
We have accumulated evidence that suggests that these systems are indeed quasars obscured by many tens of magnitudes of extinction. We have suggested that these Ultraluminous Infrared Galaxies are the formation stage of quasars, and that colliding galaxies, ultraluminous infrared galaxies, and quasars might all be linked through an evolutionary sequence where the infrared bright phase is one in which the quasar Is formed in the nucleus of a merger system, and is enshrouded in gas and dust, while the UV excess quasars are the end state of quasar evolution where most of the enveloping dust cloud has been dissipated, and the quasar is visible directly.
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From page 345... ...
The Caltech 2 micron sky survey contained one external galaxy, M31, while the AFGL sly survey contained a handful of extragalactic objects. The IRAN sky survey, with its 3 orders of magnitude improvement in sensitivity over previous surveys, and extension to 60 microns and 100 microns, drastically increased the numbers of galaxies detected purely by their infrared emission, finding ~ 0.5 galaxies/square degree, and altered our understanding of the extragalactic sly, permitting an unbiased view of the local universe in the infrared.
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From page 346... ...
The combination of the sensitivity of the IRAS survey, and the wavelength at which the infrared luminosity emerges from galaxies results in the vast majored of the ~ 20,000 extragalactic objects discovered in the IRAS Point Source Catalog being found at 60 microns. Since the IRAS survey was done at wavelengths substantially longward of the peak in stellar photospheres, those sources seen in the infrared radiate via mechanisms substantially different from those found to be bright in optical suIveys.
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From page 347... ...
o D ~ 10-5 ~ Cal to -,.\\ · IRAS GA LAX I ES - ALL ° IRAS GALAXIES - NON-VIRGO -NORMAL GALAXIES X STARBURST GALAXIES ~ SEYFERT GALAX I ES ° QUASARS $ x ~ Y~\ 10-7 lo-8 lo-l9o! 109 1010 loll LBOL [Le]
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From page 348... ...
As can be seen immediately from Table 1, all of the Ultraluminous Infrared Galaxies are rather faint optical galaxies. The ratio of infrared to visible luminosity is quite large for the ultraluminous galaxies, ranging from 50-150, as compared to 0.3 for "typical" spirals or 1-5 for "apical" infrared selected galaxies (Soifer et al.
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From page 349... ...
349 ~~' :: ~O u2 rid V, At: A!
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From page 350... ...
Only IRAS 2249-18 is classified as an HII region spectrum based on the above line ratio. PhotometIy of the nuclear regions of these galaxies reveals that the near infrared colors of these galaxies show a very large spread, spanning the entire range of colors from slightly reddened spiral gal~es to highly reddened quasars.
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From page 351... ...
The evidence for this comes from the luminosities, emission lines, near infrared colors, and luminosity to gas mass ratios. We believe that a quasar is powering the vast luminosity emerging from these objects, however the quasar is so heavily enshrouded in dust that we new the quasar primarily through its bolometric luminosity.
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From page 352... ...
%~ 1 1 ~ t04 3000 t00 10 A (Jim) .~ xlo 2 1 ~1 1 0.1 FIGIJPE 3 The energy distributions form 0.44 microns to 350 microns for the Ult~luminous Infrared Galaxies (from Sanders et al.
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From page 353... ...
1984~. What we believe the IRAS data has provided is evidence for the formative stages of the quasar, where the gas and dust that converts the luminosity of the quasar into a bright infrared source effectively acts as a strong neutral density alter to allow us to study in detail the environment surrounding the quasar without the blinding effect of the exceedingly bright central source.
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From page 354... ...
We believe that these objects are the first formative stages of quasars in the nuclei of merging gas rich spiral galaxies. Such an explanation naturally ties the formation of quasars to a violent, but rare event in the evolution of spiral galaxies.
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From page 355... ...
1976. The AFGL Four Color Infrared Sly Surve~.
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