Luminous Infrared Galaxies
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Luminous infrared galaxies or LIRGs are
galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...
with
luminosities Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...
, the measurement of brightness, above . They are also referred to as submillimeter galaxies (SMGs) through their normal method of detection. LIRGs are more abundant than
starburst galaxies A starburst galaxy is one undergoing an exceptionally high rate of star formation, as compared to the long-term average rate of star formation in the galaxy or the star formation rate observed in most other galaxies. For example, the star formatio ...
, Seyfert galaxies and quasi-stellar objects at comparable luminosity. Infrared galaxies emit more energy in the
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from aroun ...
than at all other
wavelengths In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...
combined. A LIRG's luminosity is 100 billion times that of the Sun. Galaxies with luminosities above are ultraluminous infrared galaxies (ULIRGs). Galaxies exceeding are characterised as hyper-luminous infrared galaxies (HyLIRGs). Those exceeding are extremely luminous infrared galaxies (ELIRGs). Many of the LIRGs and ULIRGs are showing interactions and disruptions. Many of these types of galaxies spawn about 100 new stars a year as compared to the
Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked ey ...
which spawns one a year; this helps create the high level of luminosity.


Discovery and characteristics

Infrared galaxies appear to be single, gas-rich spirals whose infrared luminosity is created largely by the formation of stars within them. These types of galaxies were discovered in 1983 with IRAS. A LIRG's excess infrared luminosity may also come from the presence of an
active galactic nucleus An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not pro ...
(AGN) residing at the center. These galaxies emit more energy in the
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from aroun ...
portion of the spectrum, not visible to the naked eye. The energy given off by LIRGs is comparable to that of a
quasar A quasar is an extremely luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a mass rangin ...
(a type of AGN), which formerly was known as the most energetic object in the universe. LIRGs are brighter in the infrared than in the
optical spectrum The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called '' visible light'' or simply light. A typical human eye will respond to wa ...
because the visible light is absorbed by the high amounts of gas and dust, and the dust re-emits
thermal energy The term "thermal energy" is used loosely in various contexts in physics and engineering. It can refer to several different well-defined physical concepts. These include the internal energy or enthalpy of a body of matter and radiation; heat, ...
in the infrared spectrum. LIRGs are known to exist in denser parts of the universe than non-LIRGs.


ULIRG

LIRGs are also capable of becoming Ultra Luminous Infrared Galaxys (ULIRGs) but there is no perfect timetable because not all LIRGs turn into ULIRGs,
Newtonian mechanics Newton's laws of motion are three basic Scientific law, laws of classical mechanics that describe the relationship between the motion of an object and the forces acting on it. These laws can be paraphrased as follows: # A body remains at re ...
is used in the calculations and because the constraints are not quite approximate. Studies have shown that ULIRGs are more likely to contain an AGN than LIRGs According to one study a ULIRG is just part of an evolutionary
galaxy merger Galaxy mergers can occur when two (or more) galaxies collide. They are the most violent type of galaxy interaction. The gravitational interactions between galaxies and the friction between the gas and dust have major effects on the galaxies ...
scenario. In essence, two or more
spiral galaxies Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''stars A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
, gas and dust and a central concentration of stars known as the bulge, merge to form an early stage merger. An early stage merger in this case can also be identified as a LIRG. After that, it becomes a late stage merger, which is a ULIRG. It then becomes a
quasar A quasar is an extremely luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a mass rangin ...
and in the final stage of the evolution it becomes an
elliptical galaxy An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Rea ...
. This can be evidenced by the fact that stars are much older in elliptical galaxies than those found in the earlier stages of the evolution.


HyLIRG

Hyper luminous Infrared Galaxies (HyLIRG), also referred to as HiLIRGs and HLIRGs, are considered to be some of the most luminous persistent objects in the Universe, exhibiting extremely high star formation rates, and most of which are known to harbour
Active Galactic Nuclei An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not prod ...
(AGN). They are defined as galaxies with luminosities above 1013 L, as distinct from the less luminous population of ULIRGs (L = 1012 – 1013 L). HLIRGs were first identified through follow-up observations of the IRAS mission. IRAS F10214+4724, a HyLIRG being gravitationally lensed by a foreground
elliptical galaxy An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work ''The Rea ...
, was considered to be one of the most luminous objects in the Universe having an intrinsic luminosity of ~ 2 × 1013 L. It is believed that the
bolometric luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a s ...
of this HLIRG is likely amplified by a factor of ~30 as a result of the gravitational lensing. The majority (~80%) of the mid-infrared spectrum of these objects is found to be dominated by AGN emission. However, the
starburst MicroPro International Corporation was an American software company founded in 1978 in San Rafael, California. They are best known as the publisher of WordStar, a popular early word processor for personal computers. History Founding and early su ...
(SB) activity is known to be significant in all known sources with a mean SB contribution of ~30%. Star formation rates in HLIRGs have been shown to reach ~ 3×102 – 3×103 M yr−1.


ELIRG

The Extremely Luminous Infrared Galaxy WISE J224607.57-052635.0, with a luminosity of 300 trillion suns was discovered by NASA's
Wide-field Infrared Survey Explorer Wide-field Infrared Survey Explorer (WISE, observatory code C51, Explorer 92 and SMEX-6) is a NASA infrared astronomy space telescope in the Explorers Program. It was launched in December 2009, and placed in hibernation mode in February 2 ...
(WISE), and as of May 2015 is the most luminous
galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar Sys ...
found. The galaxy belongs to a new class of objects discovered by WISE, extremely luminous infrared galaxies, or ELIRGs. Light from the WISE J224607.57-052635.0 galaxy has traveled 12.5 billion years. The black hole at its center was billions of times the mass of our sun when the universe was a tenth (1.3 billion years) of its present age of 13.8 billion years. There are three reasons the black holes in the ELIRGs could be massive. First, the embryonic black holes might be bigger than thought possible. Second, the Eddington limit was exceeded. When a black hole feeds, gas falls in and heats, emitting light. The pressure of the emitted light forces the gas outward, creating a limit to how fast the black hole can continuously absorb matter. If a black hole broke this limit, it could theoretically increase in size at a fast rate. Black holes have previously been observed breaking this limit; the black hole in the study would have had to repeatedly break the limit to grow this large. Third, the black holes might just be bending this limit, absorbing gas faster than thought possible, if the black hole is not spinning fast. If a black hole spins slowly, it will not repel its gas absorption as much. A slow-spinning black hole can absorb more matter than a fast-spinning black hole. The massive black holes in ELIRGs could be absorbing matter for a longer time. Twenty new ELIRGs, including the most luminous galaxy found to date, have been discovered. These galaxies were not found earlier because of their distance, and because dust converts their visible light into infrared light. One has been observed to have three star-forming areas.


Observations


IRAS

The Infrared Astronomical Satellite (IRAS) was the first all-sky survey which used far-infrared wavelengths, in 1983. In that survey, tens of thousands of galaxies were detected, many of which would not have been recorded in previous surveys. It is now clear that the reason the number of detections has risen is that the majority of LIRGs in the universe emitted the bulk of their energy in the
far infrared Far infrared (FIR) is a region in the infrared spectrum of electromagnetic radiation. Far infrared is often defined as any radiation with a wavelength of 15 micrometers (μm) to 1 mm (corresponding to a range of about 20  THz to ...
. Using the IRAS, scientists were able to determine the luminosity of the galactic objects discovered. The telescope was a joint project of the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...
(
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedi ...
),
Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...
(NIVR), and the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...
(SERC). Over 250,000 infrared sources were observed during this 10-month mission.


GOALS

The Great Observatories All-sky LIRG Survey (GOALS) is a multi-wavelength study of luminous infrared galaxies, incorporating observations with
NASA's Great Observatories NASA's series of Great Observatories satellites are four large, powerful space-based astronomical telescopes launched between 1990 and 2003. They were built with different technology to examine specific wavelength/energy regions of the electrom ...
and other ground and space-based telescopes. Using information from NASA's Spitzer,
Hubble The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...
,
Chandra Chandra ( sa, चन्द्र, Candra, shining' or 'moon), also known as Soma ( sa, सोम), is the Hindu god of the Moon, and is associated with the night, plants and vegetation. He is one of the Navagraha (nine planets of Hinduism) a ...
and
Galex Galaxy Evolution Explorer (GALEX or Explorer 83 or SMEX-7) was a NASA orbiting space telescope designed to observe the universe in ultraviolet wavelengths to measure the history of star formation in the universe. In addition to paving the ...
observations in a study over 200 of the most luminous infrared selected galaxies in the local universe. Approximately 180 LIRGs were identified along with over 20 ULIRGs. The LIRGs and ULIRGs targeted in GOALS span the full range of nuclear spectral types (type-1 and type 2 Active Galactic Nuclei, LINERS's, and starbursts) and interaction stages (major mergers, minor mergers, and isolated galaxies).


List

Some examples of extremely notable LIRGs, ULIRGs, HLIRGs, ELIRGs


Image gallery

File:PIA19339-MostLuminousGalaxy-WISE-J224607.57-052635.0-20150521.jpg, WISE J224607.57-052635.0 is the most luminous galaxy in the universe. (artist's impression). File:A very bright contortionist.jpg,
South America Galaxy South is one of the cardinal directions or compass points. The direction is the opposite of north and is perpendicular to both east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Proto-Germanic ''*sunþaz' ...
taken by the
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most ver ...
File:A tale of galactic collisions.jpg, 2MASX J05210136-2521450. File:Potw1245a.tif, Luminous infrared galaxy
NGC 5010 NGC 5010 is a lenticular galaxy located about 140 million light years away in the constellation Virgo (constellation), Virgo. It was discovered by John Herschel on May 9, 1831. It is considered a Luminous Infrared Galaxy (LIRG). As the galaxy has ...
. File:IRAS 19297-0406.jpg, Ultraluminous Infrared Galaxy IRAS 19297-0406 File:Starbursts versus Monsters.jpg, Luminous infrared galaxy MCG-03-04-014


References


External links


Nearby Extreme Galaxies Linked To Humble Roots
(SpaceDaily) Jun 07, 2006

(SpaceDaily) Jun 19, 2006
The Great Observatory All-sky LIRG Survey
{{DEFAULTSORT:Luminous Infrared Galaxy Active galaxy types *