Bautz–Morgan classification

The Bautz–Morgan classification was developed in 1970 by Laura P. Bautz and William Wilson Morgan to categorize galaxy clusters based on their morphology.^[1] It defines three main types: I, II, and III. Intermediate types (I-II, II-III) are also allowed. A type IV was initially proposed, but later redacted before the final paper was published.^[2]

Classification

• A type I cluster is dominated by a bright, large, supermassive cD galaxy; for example Abell 2029 and Abell 2199.
• A type II cluster contains elliptical galaxies whose brightness relative to the cluster is intermediate to that of type I and type III. The Coma Cluster is an example of a type II.
• A type III cluster has no remarkable members, such as the Virgo Cluster. Type III has two subdivisions, type IIIE and type IIIS
  • Type IIIE clusters do not contain many giant spirals
  • Type IIIS clusters contain many giant spirals
• The deprecated type IV was for clusters whose brightest members were predominantly spirals.^[2]

Examples

	Example	Type	Notes
	Abell 2199	Type I
	Abell S740	Type I-II
	Coma Cluster	Type II
	Abell 1689	Type II-III
	Virgo Cluster	Type III
		Type IIIS
		Type IIIE

See also

• Active galactic nucleus
• Galaxy morphological classification
• List of Abell clusters
• Planet
• Stellar classification