Irregular galaxy

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NGC 1427A, an example of an irregular galaxy. It is an Irr-I category galaxy about 52 Mly distant. Irregular galaxy NGC 1427A (captured by the Hubble Space Telescope).jpg
NGC 1427A, an example of an irregular galaxy. It is an Irr-I category galaxy about 52 Mly distant.

An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy. [1] Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arm structure. [2]

Contents

Collectively they are thought to make up about a quarter of all galaxies. Some irregular galaxies were once spiral or elliptical galaxies but were deformed by an uneven external gravitational force. Irregular galaxies may contain abundant amounts of gas and dust. [3] This is not necessarily true for dwarf irregulars. [4]

Irregular galaxies are commonly small, about one tenth the mass of the Milky Way galaxy, though there are also unusual cases of large irregulars like UGC 6697. Due to their small sizes, they are prone to environmental effects like colliding with large galaxies and intergalactic clouds. [5]

Types

There are three major types of irregular galaxies: [6]

Some of the irregular galaxies, especially of the Magellanic type, are small spiral galaxies that are being distorted by the gravity of a larger neighbor.

Magellanic Clouds

The Magellanic Cloud galaxies were once classified as irregular galaxies. The Large Magellanic Cloud has since been re-classified as type SBm (barred Magellanic spiral). [8] The Small Magellanic Cloud remains classified as an irregular galaxy of type Im under current galaxy morphological classification, although it does contain a bar structure.

See also

Related Research Articles

<span class="mw-page-title-main">Hubble sequence</span> Galaxy morphological classification scheme advocated by Edwin Hubble

The Hubble sequence is a morphological classification scheme for galaxies published by Edwin Hubble in 1926. It is often colloquially known as the Hubble tuning-fork diagram because the shape in which it is traditionally represented resembles a tuning fork. It was invented by John Henry Reynolds and Sir James Jeans.

<span class="mw-page-title-main">Elliptical galaxy</span> Spherical or ovoid mass of stars

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 Realm of the Nebulae, along with spiral and lenticular galaxies. Elliptical (E) galaxies are, together with lenticular galaxies (S0) with their large-scale disks, and ES galaxies with their intermediate scale disks, a subset of the "early-type" galaxy population.

<span class="mw-page-title-main">Lenticular galaxy</span> Class of galaxy between an elliptical galaxy and a spiral galaxy

A lenticular galaxy is a type of galaxy intermediate between an elliptical and a spiral galaxy in galaxy morphological classification schemes. It contains a large-scale disc but does not have large-scale spiral arms. Lenticular galaxies are disc galaxies that have used up or lost most of their interstellar matter and therefore have very little ongoing star formation. They may, however, retain significant dust in their disks. As a result, they consist mainly of aging stars. Despite the morphological differences, lenticular and elliptical galaxies share common properties like spectral features and scaling relations. Both can be considered early-type galaxies that are passively evolving, at least in the local part of the Universe. Connecting the E galaxies with the S0 galaxies are the ES galaxies with intermediate-scale discs.

<span class="mw-page-title-main">IC 10</span> Irregular starburst galaxy in the constellation Cassiopeia

IC 10 is an irregular galaxy in the constellation Cassiopeia. It was discovered by Lewis Swift in 1887 and in 1935 Nicholas Mayall became the first to suggest that the object is extragalactic. Edwin Hubble suspected it might belong to the Local Group of galaxies, but its status remained uncertain for decades. The radial velocity of IC 10 was measured in 1962, and it was found to be approaching the Milky Way at approximately 350 km/s, strengthening the evidence for its membership in the Local Group. Its membership in the group was finally confirmed in 1996 by direct measurements of its distance based on observations of Cepheids; most estimates place the galaxy 2–3 million light years from Earth, with some estimates ranging from 1.5–4.5 million light years. Despite its closeness, the galaxy is rather difficult to study because it lies near the plane of the Milky Way and is therefore heavily obscured by interstellar matter.

<span class="mw-page-title-main">Galaxy morphological classification</span> System for categorizing galaxies based on appearance

Galaxy morphological classification is a system used by astronomers to divide galaxies into groups based on their visual appearance. There are several schemes in use by which galaxies can be classified according to their morphologies, the most famous being the Hubble sequence, devised by Edwin Hubble and later expanded by Gérard de Vaucouleurs and Allan Sandage. However, galaxy classification and morphology are now largely done using computational methods and physical morphology.

<span class="mw-page-title-main">Barred spiral galaxy</span> Spiral galaxy with a central bar-shaped structure composed of stars

A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies in the local universe, and generally affect both the motions of stars and interstellar gas within spiral galaxies and can affect spiral arms as well. The Milky Way Galaxy, where the Solar System is located, is classified as a barred spiral galaxy.

<span class="mw-page-title-main">Dwarf galaxy</span> Small galaxy composed of up to several billion stars

A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.

<span class="mw-page-title-main">NGC 1569</span> Galaxy in the constellation Camelopardalis

NGC 1569 is a dwarf irregular galaxy in Camelopardalis. The galaxy is relatively nearby and consequently, the Hubble Space Telescope can easily resolve the stars within the galaxy. The distance to the galaxy was previously believed to be only 2.4 Mpc. However, in 2008 scientists studying images from Hubble calculated the galaxy's distance at nearly 11 million light-years away, about 4 million light-years farther than previously thought, meaning it is a member of the IC 342 group of galaxies.

<span class="mw-page-title-main">NGC 6822</span> Galaxy in the constellation Sagittarius

NGC 6822 is a barred irregular galaxy approximately 1.6 million light-years away in the constellation Sagittarius. Part of the Local Group of galaxies, it was discovered by E. E. Barnard in 1884, with a six-inch refractor telescope. It is the closest non-satellite galaxy to the Milky Way, but lies just outside its virial radius. It is similar in structure and composition to the Small Magellanic Cloud. It is about 7,000 light-years in diameter.

<span class="mw-page-title-main">Interacting galaxy</span> Galaxies with interacting gravitational fields

Interacting galaxies are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision, which may lead to a galaxy merger.

David Dunlap Observatory Catalogue, known as the DDO or A Catalogue of Dwarf Galaxies, is a catalogue of dwarf galaxies that was compiled by Sidney van den Bergh and published by the David Dunlap Observatory in 1959.

<span class="mw-page-title-main">Arp 107</span> Interacting galaxy in the constellation Leo Minor

Arp 107 is a pair of interacting galaxies located about 450 million light-years away in the constellation Leo Minor. The galaxies are in the process of colliding and merging.

<span class="mw-page-title-main">NGC 1427A</span> Galaxy in the constellation Fornax

NGC 1427A, also known as ESO 358-49, or ESO 358- G 049, is an irregular galaxy in the constellation Fornax. Its distance modulus has been estimated using the globular cluster luminosity function to be 31.01 ± 0.21 which is about 52 Mly. It is the brightest dwarf irregular member of the Fornax cluster and is in the foreground of the cluster's central galaxy NGC 1399.

A Magellanic spiral galaxy is a spiral galaxy with only one spiral arm. Magellanic spiral galaxies are classified as the type Sm ; the prototype galaxy and namesake for Magellanic spirals is the Large Magellanic Cloud, an SBm galaxy. They are usually smaller dwarf galaxies and can be considered to be intermediate between dwarf spiral galaxies and irregular galaxies.

<span class="mw-page-title-main">UGC 2885</span> Large barred spiral galaxy in the constellation Perseus

UGC 2885 is a large barred spiral galaxy of type SA(rs)c in the constellation Perseus. It is 232 million light-years (71 Mpc) from Earth and measures 463,000 ly (142,000 pc) across, making it one of the largest known spiral galaxies. It is also a possible member of the Pisces-Perseus supercluster.

<span class="mw-page-title-main">NGC 4707</span> Galaxy in constellation Canes Venatici

NGC 4707 is an irregular galaxy in the constellation of Canes Venatici. It was discovered by John Herschel on 5 June 1834, and was described by John Louis Emil Dreyer, the compiler of the New General Catalogue, as a "small, stellar" galaxy.

<span class="mw-page-title-main">PGC 44691</span> Spiral galaxy in constellation Coma Berenices

PGC 44691 is a spiral galaxy located about 350 million light-years away in the constellation Coma Berenices. It belongs to a galaxy cluster known as the Coma Cluster. In 1994, the Hubble Space Telescope observed PGC 44691 and the nearby elliptical galaxy NGC 4881 to infer the distance to the Coma Cluster.

<span class="mw-page-title-main">IC 4710</span> Irregular galaxy in the constellation Pavo

IC 4710 is a galaxy in southern constellation of Pavo, roughly 34 million light-years away.

<span class="mw-page-title-main">IC 3583</span> Irregular Galaxy in the constellation of Virgo

IC 3583 is an irregular galaxy some 30 million light-years away in the constellation of Virgo. It was discovered by Isaac Roberts on April 29, 1892.

<span class="mw-page-title-main">IC 4662</span> Irregular Galaxy in the constellation Pavo

IC 4662, also known as ESO 102-14 is an irregular galaxy located in the constellation Pavo 7.96 million light years away. It was discovered by Robert T. A. Innes in 1901. It has a diameter of 7000 light years and an angular size of 3.2' x 1.9'.

References

  1. ↑ Butz, Stephen D. (2002). Science of Earth Systems. Cengage Learning. p. 107. ISBN   978-0-7668-3391-3.
  2. ↑ Morgan, W. W. & Mayall, N. U. (1957). "A Spectral Classification of Galaxies." Publications of the Astronomical Society of the Pacific.69 (409): 291–303.
  3. ↑ "Faulkes Telescope Educational Guide – Irregular Galaxies". Archived from the original on 17 October 2022.
  4. ↑ Walter, F. et al. Astophys J 661, 102 - 114, 2007
  5. ↑ Elmegreen, Debra Meloy; Elmegreen, Bruce G. (2002). "Galaxies" . In Dasch, Pat (ed.). Space Sciences. Planetary Science and Astronomy. Vol. 2. Macmillan Reference USA. pp. 50–56. Retrieved 25 September 2017– via Gale Virtual Reference Library.
  6. ↑ Gallagher, J. S. & Hunter, D. A. (1984). "Structure and Evolution of Irregular Galaxies." Annual Review of Astronomy and Astrophysics.22: 37-74. doi : 10.1146/annurev.aa.22.090184.000345
  7. ↑ Grebel, Eva K. (2004). The evolutionary history of Local Group irregular galaxies. in McWilliam, Andrew; Rauch, Michael (eds) Origin and evolution of the elements. Cambridge University Press. p. 234-254. ISBN   978-0-521-75578-8.
  8. ↑ Corso, G. and Buscombe, W. The Observatory, 90, 229 - 233 (1970) On the spiral structure of the Large Magellanic Cloud
  9. ↑ "Feeling blue". www.spacetelescope.org. Archived from the original on 5 November 2018. Retrieved 5 November 2018.
  10. ↑ "A frenzy of stars". www.spacetelescope.org. Archived from the original on 25 October 2020. Retrieved 26 February 2018.
  11. ↑ "Surveying the cosmos". www.spacetelescope.org. Archived from the original on 18 July 2020. Retrieved 19 June 2017.
  12. ↑ "Spotlight on IC 3583". www.spacetelescope.org. Archived from the original on 17 August 2019. Retrieved 28 November 2016.
  13. ↑ "A lopsided lynx". www.spacetelescope.org. Archived from the original on 21 November 2020. Retrieved 9 August 2016.
  14. ↑ "A distinctly disorganised dwarf". Archived from the original on 25 October 2020. Retrieved 29 March 2016.
  15. ↑ "Meeting the neighbours". www.spacetelescope.org. ESA/Hubble. Archived from the original on 27 November 2020. Retrieved 8 June 2015.
  16. ↑ "A spattering of blue". www.spacetelescope.org. ESA/Hubble. Archived from the original on 5 June 2019. Retrieved 8 September 2014.
  17. ↑ "A cosmic optical illusion". ESA/Hubble Picture of the Week. Archived from the original on 7 January 2018. Retrieved 20 August 2013.
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