Editing Irregular galaxy (section)

==Types==
There are three major types of irregular galaxies:<ref>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}}</ref>

* An Irr-I galaxy ('''Irr I''') is an irregular galaxy that features some [[structure]] but not enough to place it cleanly into the Hubble sequence. 
**Subtypes with some spiral structure are called [[Magellanic spiral|Sm]] galaxies
**Subtypes without spiral structure are called '''Im''' galaxies.

* An Irr-II galaxy ('''Irr II''') is an irregular galaxy that does not appear to feature any structure that can place it into the Hubble sequence.

{{anchor|dwarf_irregular_anchor}}
* A dI-galaxy (or '''dIrr''') is a [[dwarf galaxy|dwarf]] irregular galaxy.<ref>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}}.</ref> This type of galaxy is now thought to be important to understand the overall evolution of galaxies, as they tend to have a low level of [[metallicity]] and relatively high levels of gas, and are thought to be similar to the earliest galaxies that populated the Universe. They may represent a local (and therefore more recent) version of the [[Faint blue galaxy|faint blue galaxies]] known to exist in [[Hubble Ultra-Deep Field|deep field galaxy surveys]]. These types of irregular galaxies also have high amounts of [[dark matter]]. <ref>{{Cite journal |last1=Rivas |first1=Jonathan |last2=Flores-Velazquez |first2=Jeysen |last3=Wheeler |first3=Coral |date=2024-02-01 |title=Major Merger between a Classical Dwarf Irregular Galaxy and its Massive Ultra-Faint Satellite |journal=American Astronomical Society Meeting Abstracts |url=https://ui.adsabs.harvard.edu/abs/2024AAS...24340418R/exportcitation |volume=243 |pages=404.18|bibcode=2024AAS...24340418R }}</ref>

Irregular galaxies are considered late-type along with [[Spiral galaxy|spiral galaxies]] as opposed to early type [[elliptical galaxies]]. <ref>{{Cite web |date=2023-12-15 |title=Hubble Looks at a Late-type Galaxy – NASA Science |url=https://science.nasa.gov/missions/hubble/hubble-looks-at-a-late-type-galaxy/#:~:text=The%20terminology%20%E2%80%9Clate-type%E2%80%9D,type%E2%80%9D%20refers%20to%20elliptical%20galaxies. |access-date=2025-01-27 |language=en-US}}</ref>

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