Cosmic infrared background

Cosmic infrared background is caused by stellar dust.

Recognizing the cosmological importance of the darkness of the night sky (Olbers' paradox) and the first speculations on an extragalactic background light dates back to the first half of the 19th century. Despite its importance, the first attempts were made only in the 1950-60s to derive the value of the visual background due to galaxies, at that time based on the integrated starlight of these stellar systems. In the 1960s the absorption of starlight by dust was already taken into account, but without considering the re-emission of this absorbed energy in the infrared. At that time Jim Peebles pointed out, that in a Big Bang-created Universe there must have been a cosmic infrared background (CIB) - different from the cosmic microwave background - that can account for the formation and evolution of stars and galaxies.

In order to produce today's metallicity, early galaxies must have been significantly more powerful than they are today. In the early CIB models the absorption of starlight was neglected, therefore in these models the CIB peaked between 1-10μm wavelengths. These early models have already shown correctly that the CIB was most probably fainter than its foregrounds, and so it was very difficult to observe. Later the discovery and observations of high luminosity infrared galaxies in the vicinity of the Milky Way showed, that the peak of the CIB is most likely at longer wavelengths (around 50μm), and its full power could be ~1-10% of that of the CMB.

As Martin Harwit emphasized, the CIB is very important in the understanding of some special astronomical objects, like quasars or ultraluminous infrared galaxies, which are very bright in the infrared. He also pointed out, that the CIB cause a significant attenuation for very high energy electrons, protons and gamma-rays of the cosmic radiation through inverse Compton scattering, photopion and electron-positron pair production.

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