HII galaxy

{{short description|Galaxy spectroscopically similar to HII region}}

An HII galaxy is a very luminous dwarf starburst galaxy. Generally, HII galaxies have a low metallicity and high percentage of neutral hydrogen. There is generally believed to be a relationship between luminosity and disturbed morphology, suggesting that the starburst activity in the galaxy is caused by tidal interactions.{{Cite journal|last1=Telles|first1=Eduardo|last2=Terlevich|first2=Roberto|date=1995-07-01|title=The environment of HII galaxies|url=https://academic.oup.com/mnras/article/275/1/1/1003663|journal=Monthly Notices of the Royal Astronomical Society|language=en|volume=275|issue=1|pages=1–8|doi=10.1093/mnras/275.1.1|issn=0035-8711|doi-access=free|arxiv=astro-ph/9501084}} The distribution of luminosities tends to cluster around two different extremes: those with a high luminosity and highly disturbed morphology, and those with a low luminosity and fairly regular and symmetric morphology.{{Cite journal|last1=Telles|first1=Eduardo|last2=Melnick|first2=Jorge|last3=Terlevich|first3=Roberto|date=1997-06-11|title=The morphology of H II galaxies|url=https://academic.oup.com/mnras/article/288/1/78/1067787|journal=Monthly Notices of the Royal Astronomical Society|language=en|volume=288|issue=1|pages=78–107|doi=10.1093/mnras/288.1.78|issn=0035-8711|doi-access=free|arxiv=astro-ph/9701062}} Those with high luminosities are labelled by some as type I HII galaxies and those with lower luminosities as type II HII galaxies. There is also a general correlation between metallicity and mass of the galaxies.{{Cite journal|url=http://adsabs.harvard.edu/full/1991A&AS...89..389M|title=1991A&AS...89..389M Page 389|journal=Astronomy and Astrophysics Supplement Series|bibcode=1991A&AS...89..389M |access-date=2020-04-11 |last1=Maza |first1=J. |last2=Ruiz |first2=M. T. |last3=Pena |first3=M. |last4=Gonzalez |first4=L. E. |last5=Wischnjewsky |first5=M. |date=1991 |volume=89 |page=389 }} The name of HII galaxies comes from their spectroscopic properties which are more or less indistinguishable from that of HII regions.