Cosmic infrared background
Encyclopedia
Cosmic infrared background (CIB) is a mysterious infrared light coming from outer space
. It is slowly being resolved into specific sources by infrared telescope
s. In some ways it is analogous to the cosmic microwave background, but at shorter wavelengths.
) 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.
In the early 1980s there were only upper limits available for the CIB. The real observations of the CIB began after the era of astronomical satellites working in the infrared, started by the Infrared Astronomy Satellite (IRAS), and followed by the Cosmic Background Explorer (COBE), the Infrared Space Observatory
(ISO) and the by the Spitzer Space Telescope
. Exploration of the CIB was continued by the Herschel Space Observatory
, launched in 2009.
A summary on the history of CIB research can be found in the review papers by M.G. Hauser and E. Dwek (2001) and A. Kashlinsky (2005).
of the galaxies found in our cosmic neighborhood. However, these simple models could not reproduce the observed features of the CIB. In the baryonic material of the Universe there are two sources of large amounts of energy: nuclear fusion and gravitation.
Nuclear fusion takes place inside the stars, and we can really see this light redshifted: this is the main source of the cosmic ultraviolet- and visual background. However, a significant amount of this starlight is not observed directly. Dust in the host galaxies can absorb it and re-emit it in the infrared, contributing to the CIB. Although most of today's galaxies contain little dust (e.g. elliptical galaxies are practically dustless), there are some special stellar systems even in our vicinity which are extremely bright in the infrared and at the same time faint (often almost invisible) in the optical. These ultraluminous infrared galaxies (ULIRGs) are just in a very active star formation
period: they are just in a collision or in a merge with another galaxy. In the optical this is hidden by the huge amount of dust, and the galaxy is bright in the infrared due to the same reason. Galaxy collisions and mergers were more frequent in the cosmic past: the global star formation rate of the Universe peaked around z=1..2, and was 10...50 times the average value today. These galaxies in the z=1...2 redshift range gives the 50...70% of the full brightness of the CIB.
Another important component of the CIB is the infrared emission by quasars. In these systems most of the gravitational potential energy of the matter falling into the central black hole
is converted into X-rays, which would escape unless it is absorbed by the dust torus of the accretion disc
. This absorbed light is again re-emitted in the infrared, and in total gives about 20-30% of the full power of the CIB; however at some specific wavelengths this is the dominant source of CIB energy.
These components must be separated for a clear CIB detection.
The first, and still the most extensive, direct CIB measurements were performed by the DIRBE instrument of the COBE
satellite. After the removal of the precisely determined zodiacal emission contribution (which was based on the measured annual variation) the remaining power at longer infrared wavelength contained basically two components: the CIB and the Galactic cirrus emission. The infrared surface brightness of the Galactic cirrus must correlate with the neutral hydrogen column densities, since they originate from the same, low density structure. After the removal of the HI-correlated part, the remaining surface brightness was identified as the cosmic infrared background at 60, 100, 140 and 240μm. At shorter wavelengths the CIB level could not be correctly determined.
Later, short wavelength DIRBE measurements at 2.2 and 3.5μ were combined with the Two Micron Sky Survey (2MASS
) source count data, and this led to the detection of the
CIB at these two wavelengths.
power spectrum. The detection of fluctuations is easier than the direct CIB measurements, since one does not need to determine the absolute photometric zero point - fluctuations can be derived from differential measurements. On the other hand, fluctuations do not provide an immediate information on the CIB brightness. The measured fluctuation amplitudes either has to be confronted with a CIB model that has a prediction for the fluctuation / absolute level ratio, or it has to be compared with integrated differential light levels of source counts
at the same wavelength.
The power spectrum of the CIB is usually presented in a spatial frequency [arcmin−1] vs. fluctuation power [Jy2 sr−1] diagram. It is contaminated by the presence of the power spectrum of foreground components, so that the total power spectrum is:
P(f) = Φ(f)x[PCIB(f) + Pcirr(f) + Pze(f) + Pn(f)]
where P(f), PCIB(f), Pcirr, Pze(f) and Pn(f) are the total, CIB, Galactic cirrus
, zodiacal emission and noise (instrument noise) power spectrum components, respectively, and Φ is the power spectrum of the telescope's point spread function
.
For most of the infrared zodiacal emission fluctuation are negligible in the "cosmic windows", far from the ecliptic
plane.
In the far-infrared the CIB power spectrum can be effectively used to separate it from its strongest foreground, the Galactic cirrus emission. The cirrus emission has a characteristic power spectrum of a power-law (that of a fractal
spatial structure) P(f) = P0(f/f0)α, where P is the fluctuation power at the spatial frequency f, P0 is the fluctuation power at the reference spatial frequency f0, and α is the spectral index. α was found to be α≈-3, which is much steeper than the power spectrum of the CIB at low spatial frequencies. The cirrus component can be identified in the power spectrum at low spatial frequencies and then removed from the whole spatial frequency range. The remaining power spectrum - after a careful correction for instrument effects - should be that of the CIB.
Autocorrelation and power spectrum studies resulted in the CIB fluctuation amplitudes at 1.25, 2.2, 3.5, 12-100μm based on the COBE
/DIRBE measurements, and later at 90 and 170μm, based on the observations of the ISOPHOT instrument of the Infrared Space Observatory
. Recently, the clustering of the galaxies have also been identified in the power spectrum at 160μm using this method.
gives the most extensive picture about the sources building up the CIB. In a source count one tries to detect as many point/compact sources in a certain field of view as possible: this is usually done at multiple wavelengths and is often complemented by other data, e.g. photometry at visual or sub-millimeter wavelengths. In this way, one has information on the broad band spectral characteristics of the detected sources, too. The detected point sources has to be distinguished from other contaminating sources, e.g. minor bodies in the Solar System, Galactic stars and cirrus knots (local density enhancements in the Galactic cirrus emission).
Source counts were important tasks for the recent infrared missions like 2MASS
or the Infrared Space Observatory
(ISO), and is still one of the most important questions the current and near future infrared space instruments (the Spitzer Space Telescope
and the Herschel Space Observatory
). While ISO was able to resolve about 3-10% of the total CIB light into individual sources (depending on the wavelength), Spitzer measurements have already detected ~30% of the CIB as sources, and this ratio is expected to be ~90% at some wavelengths with the Herschel Space Observatory
.
Source count results support the "fast evolution" galaxy models. In these models galaxies nowadays look significantly different than they were at z=1...2, when they were coming through an intense star-formation phase. The source count results exclude the "steady state" scenarios, where z=1...2 galaxies look similar to those we see today in our cosmic neighborhood.
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....
. It is slowly being resolved into specific sources by infrared telescope
Infrared telescope
An infrared telescope is a telescope that uses infrared light to detect celestial bodies.Infrared light is one of several types of radiation present in the electromagnetic spectrum....
s. In some ways it is analogous to the cosmic microwave background, but at shorter wavelengths.
History
Recognizing the cosmological importance of the darkness of the night sky (Olbers' paradoxOlbers' paradox
In astrophysics and physical cosmology, Olbers' paradox is the argument that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe. It is one of the pieces of evidence for a non-static universe such as the current Big Bang model. The argument is also...
) and the first speculations on an extragalactic background light
Extragalactic background light
The Extragalactic Background Light or simply the "extragalactic background" is the faint diffuse light of the night sky, consisting of the combined flux of all extragalactic sources...
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
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
. At that time Jim Peebles
Jim Peebles
Phillip James Edwin Peebles is a Canadian-American physicist and theoretical cosmologist who is currently the Albert Einstein Professor Emeritus of Science at Princeton University. Peebles was born in Winnipeg and completed his bachelor's degree at the University of Manitoba...
pointed out, that in a Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
-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
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
, 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
CMB
CMB can mean:*The IATA airport code for Bandaranaike International Airport, Colombo – Sri Lanka's only international airport*C.M.B., the debut album of American R&B and pop group Color Me Badd...
.
As Martin Harwit
Martin Harwit
Martin Harwit is a Czech-American astronomer, author, and was director of the National Air and Space Museum in Washington, D.C. from 1987 to 1995...
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
Compton scattering
In physics, Compton scattering is a type of scattering that X-rays and gamma rays undergo in matter. The inelastic scattering of photons in matter results in a decrease in energy of an X-ray or gamma ray photon, called the Compton effect...
, photopion and electron-positron pair production.
In the early 1980s there were only upper limits available for the CIB. The real observations of the CIB began after the era of astronomical satellites working in the infrared, started by the Infrared Astronomy Satellite (IRAS), and followed by the Cosmic Background Explorer (COBE), the Infrared Space Observatory
Infrared Space Observatory
The Infrared Space Observatory was a space telescope for infrared light designed and operated by the European Space Agency , in cooperation with ISAS and NASA...
(ISO) and the by the Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
. Exploration of the CIB was continued by the Herschel Space Observatory
Herschel Space Observatory
The Herschel Space Observatory is a European Space Agency space observatory sensitive to the far infrared and submillimetre wavebands. It is the largest space telescope ever launched, carrying a single mirror of in diameter....
, launched in 2009.
A summary on the history of CIB research can be found in the review papers by M.G. Hauser and E. Dwek (2001) and A. Kashlinsky (2005).
Origin of the cosmic infrared background
One of the most important questions about the CIB is the source of its energy. In the early models the CIB was built up from the redshifted spectraElectromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
of the galaxies found in our cosmic neighborhood. However, these simple models could not reproduce the observed features of the CIB. In the baryonic material of the Universe there are two sources of large amounts of energy: nuclear fusion and gravitation.
Nuclear fusion takes place inside the stars, and we can really see this light redshifted: this is the main source of the cosmic ultraviolet- and visual background. However, a significant amount of this starlight is not observed directly. Dust in the host galaxies can absorb it and re-emit it in the infrared, contributing to the CIB. Although most of today's galaxies contain little dust (e.g. elliptical galaxies are practically dustless), there are some special stellar systems even in our vicinity which are extremely bright in the infrared and at the same time faint (often almost invisible) in the optical. These ultraluminous infrared galaxies (ULIRGs) are just in a very active star formation
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
period: they are just in a collision or in a merge with another galaxy. In the optical this is hidden by the huge amount of dust, and the galaxy is bright in the infrared due to the same reason. Galaxy collisions and mergers were more frequent in the cosmic past: the global star formation rate of the Universe peaked around z=1..2, and was 10...50 times the average value today. These galaxies in the z=1...2 redshift range gives the 50...70% of the full brightness of the CIB.
Another important component of the CIB is the infrared emission by quasars. In these systems most of the gravitational potential energy of the matter falling into the central black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
is converted into X-rays, which would escape unless it is absorbed by the dust torus of the accretion disc
Accretion disc
An accretion disc is a structure formed by diffuse material in orbital motion around a central body. The central body is typically a star. Gravity causes material in the disc to spiral inward towards the central body. Gravitational forces compress the material causing the emission of...
. This absorbed light is again re-emitted in the infrared, and in total gives about 20-30% of the full power of the CIB; however at some specific wavelengths this is the dominant source of CIB energy.
Foregrounds
The most important foreground components of the CIB are the following:- Zodiacal emission: the thermal emission of microscopic dust particles in the Solar SystemSolar SystemThe Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
(from near- to mid-infrared) - Thermal emission of small asteroids in the Solar SystemSolar SystemThe Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
(from near- to mid-infrared) - Galactic cirrus emissionInfrared CirrusInfrared cirrus are filamentary structures seen in infrared light. The name is given because the structure looks cloud-like in appearance. First detected by the Infrared Astronomy Satellite at wavelengths of 60 and 100 micrometres.-External links:...
(far-infrared) - Faint GalacticGalacticGalactic is a funk and jazz jam band from New Orleans, Louisiana, United States.-Origins and background:Originally formed in 1994 as an octet and including singer Chris Lane and guitarist Rob Gowen, the group was soon pared down to a sextet of: guitarist Jeff Raines, bassist Robert Mercurio,...
starStarA star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s (in the near-infrared, λ<20μm) - Infrared emission of intracluster dustIntracluster mediumIn astronomy, the intracluster medium is the superheated plasma present at the center of a galaxy cluster. This is gas heated to temperatures of between roughly 10 and 100 megakelvins and consisting mainly of ionised hydrogen and helium, containing most of the baryonic material in the cluster...
in the Local GroupLocal GroupThe Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy... - The cosmic microwave background - although physically it is not a "foreground" - is also considered as an important contaminating source of emission at very long infrared wavelengths (λ>300μm)
These components must be separated for a clear CIB detection.
Observation of the cosmic infrared background
The detection of the CIB is both observationally and astrophysically very challenging. It has a very few characteristics which can be used to separate it from the foregrounds. One major point is, that the CIB must be isotropic, i.e. one has to measure the same CIB value all over the sky. It also lacks suspicious spectral features, since the final shape of its spectrum is the sum of the spectra of sources in the line of sight at various redshifts.Direct detection
Direct measurements are simple, but very difficult. One just has to measure the total incoming power, and determine the contribution of each sky background component. The measurement has to be repeated in many directions to determine the contribution of the foregrounds. After the removal of all other components the remaining power - if it is the same constant value in any direction - is the CIB at that specific wavelength. In practice, one needs an instrument which is able to perform absolute photometry, i.e. it has some mechanism to fully block incoming light for an accurate zero level determination (cold shutter). Since the instrument parts, including the shutter, have non-zero temperatures and emit in the infrared, this is a very difficult task.The first, and still the most extensive, direct CIB measurements were performed by the DIRBE instrument of the COBE
COBE
The COsmic Background Explorer , also referred to as Explorer 66, was a satellite dedicated to cosmology. Its goals were to investigate the cosmic microwave background radiation of the universe and provide measurements that would help shape our understanding of the cosmos.This work provided...
satellite. After the removal of the precisely determined zodiacal emission contribution (which was based on the measured annual variation) the remaining power at longer infrared wavelength contained basically two components: the CIB and the Galactic cirrus emission. The infrared surface brightness of the Galactic cirrus must correlate with the neutral hydrogen column densities, since they originate from the same, low density structure. After the removal of the HI-correlated part, the remaining surface brightness was identified as the cosmic infrared background at 60, 100, 140 and 240μm. At shorter wavelengths the CIB level could not be correctly determined.
Later, short wavelength DIRBE measurements at 2.2 and 3.5μ were combined with the Two Micron Sky Survey (2MASS
2MASS
Observations for the Two Micron All-Sky Survey began in 1997 and were completed in 2001 at two telescopes located one each in the northern and southern hemispheres to ensure coverage of the entire sky...
) source count data, and this led to the detection of the
CIB at these two wavelengths.
Fluctuation studies
Since the CIB is an accumulated light of individual sources there is always a somewhat different number of sources in different directions in the field of view of the observer. This cause a variation (fluctuation) in the total amount of observed incoming flux. Among the different line of sights. These fluctuations are traditionally described by the two dimensional autocorrelation function, or by the corresponding FourierFourier
Fourier most commonly refers to Joseph Fourier , French mathematician and physicist, or the mathematics, physics, and engineering terms named in his honor for his work on the concepts underlying them:In mathematics:...
power spectrum. The detection of fluctuations is easier than the direct CIB measurements, since one does not need to determine the absolute photometric zero point - fluctuations can be derived from differential measurements. On the other hand, fluctuations do not provide an immediate information on the CIB brightness. The measured fluctuation amplitudes either has to be confronted with a CIB model that has a prediction for the fluctuation / absolute level ratio, or it has to be compared with integrated differential light levels of source counts
Source counts
The source counts distribution of radio-sources from a radio-astronomical survey is the cumulative distribution of the number of sources brighter than a given flux density...
at the same wavelength.
The power spectrum of the CIB is usually presented in a spatial frequency [arcmin−1] vs. fluctuation power [Jy2 sr−1] diagram. It is contaminated by the presence of the power spectrum of foreground components, so that the total power spectrum is:
P(f) = Φ(f)x[PCIB(f) + Pcirr(f) + Pze(f) + Pn(f)]
where P(f), PCIB(f), Pcirr, Pze(f) and Pn(f) are the total, CIB, Galactic cirrus
Infrared Cirrus
Infrared cirrus are filamentary structures seen in infrared light. The name is given because the structure looks cloud-like in appearance. First detected by the Infrared Astronomy Satellite at wavelengths of 60 and 100 micrometres.-External links:...
, zodiacal emission and noise (instrument noise) power spectrum components, respectively, and Φ is the power spectrum of the telescope's point spread function
Point spread function
The point spread function describes the response of an imaging system to a point source or point object. A more general term for the PSF is a system's impulse response, the PSF being the impulse response of a focused optical system. The PSF in many contexts can be thought of as the extended blob...
.
For most of the infrared zodiacal emission fluctuation are negligible in the "cosmic windows", far from the ecliptic
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
plane.
In the far-infrared the CIB power spectrum can be effectively used to separate it from its strongest foreground, the Galactic cirrus emission. The cirrus emission has a characteristic power spectrum of a power-law (that of a fractal
Fractal
A fractal has been defined as "a rough or fragmented geometric shape that can be split into parts, each of which is a reduced-size copy of the whole," a property called self-similarity...
spatial structure) P(f) = P0(f/f0)α, where P is the fluctuation power at the spatial frequency f, P0 is the fluctuation power at the reference spatial frequency f0, and α is the spectral index. α was found to be α≈-3, which is much steeper than the power spectrum of the CIB at low spatial frequencies. The cirrus component can be identified in the power spectrum at low spatial frequencies and then removed from the whole spatial frequency range. The remaining power spectrum - after a careful correction for instrument effects - should be that of the CIB.
Autocorrelation and power spectrum studies resulted in the CIB fluctuation amplitudes at 1.25, 2.2, 3.5, 12-100μm based on the COBE
COBE
The COsmic Background Explorer , also referred to as Explorer 66, was a satellite dedicated to cosmology. Its goals were to investigate the cosmic microwave background radiation of the universe and provide measurements that would help shape our understanding of the cosmos.This work provided...
/DIRBE measurements, and later at 90 and 170μm, based on the observations of the ISOPHOT instrument of the Infrared Space Observatory
Infrared Space Observatory
The Infrared Space Observatory was a space telescope for infrared light designed and operated by the European Space Agency , in cooperation with ISAS and NASA...
. Recently, the clustering of the galaxies have also been identified in the power spectrum at 160μm using this method.
Source counts
Source countsSource counts
The source counts distribution of radio-sources from a radio-astronomical survey is the cumulative distribution of the number of sources brighter than a given flux density...
gives the most extensive picture about the sources building up the CIB. In a source count one tries to detect as many point/compact sources in a certain field of view as possible: this is usually done at multiple wavelengths and is often complemented by other data, e.g. photometry at visual or sub-millimeter wavelengths. In this way, one has information on the broad band spectral characteristics of the detected sources, too. The detected point sources has to be distinguished from other contaminating sources, e.g. minor bodies in the Solar System, Galactic stars and cirrus knots (local density enhancements in the Galactic cirrus emission).
Source counts were important tasks for the recent infrared missions like 2MASS
2MASS
Observations for the Two Micron All-Sky Survey began in 1997 and were completed in 2001 at two telescopes located one each in the northern and southern hemispheres to ensure coverage of the entire sky...
or the Infrared Space Observatory
Infrared Space Observatory
The Infrared Space Observatory was a space telescope for infrared light designed and operated by the European Space Agency , in cooperation with ISAS and NASA...
(ISO), and is still one of the most important questions the current and near future infrared space instruments (the Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
and the Herschel Space Observatory
Herschel Space Observatory
The Herschel Space Observatory is a European Space Agency space observatory sensitive to the far infrared and submillimetre wavebands. It is the largest space telescope ever launched, carrying a single mirror of in diameter....
). While ISO was able to resolve about 3-10% of the total CIB light into individual sources (depending on the wavelength), Spitzer measurements have already detected ~30% of the CIB as sources, and this ratio is expected to be ~90% at some wavelengths with the Herschel Space Observatory
Herschel Space Observatory
The Herschel Space Observatory is a European Space Agency space observatory sensitive to the far infrared and submillimetre wavebands. It is the largest space telescope ever launched, carrying a single mirror of in diameter....
.
Source count results support the "fast evolution" galaxy models. In these models galaxies nowadays look significantly different than they were at z=1...2, when they were coming through an intense star-formation phase. The source count results exclude the "steady state" scenarios, where z=1...2 galaxies look similar to those we see today in our cosmic neighborhood.
External links
- Cosmic InfraRed Background Radiation
- TeV Blazars and Cosmic Infrared Background Radiation, F.A. Aharonian, 2001
- Astronomers Discover an Infrared Background Glow in the Universe, Release Number: STScI-1998-01