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NGC 3921
NGC 3921
	NGC 3921, imaged by the Hubble Space Telescope
Observation data (J2000 epoch)
Constellation	Ursa Major
Right ascension	11h 51m 06.863s
Declination	+55° 04′ 43.38″
Redshift	0.019667
Heliocentric radial velocity	5896 km/s
Distance	277.9 Mly (85.19 Mpc)
Apparent magnitude (V)	12.64
Apparent magnitude (B)	13.4
Absolute magnitude (V)	−22.09
Characteristics
Type	(R')SA0/a(s) pec
Size	180,200 ly (55,240 pc)
Apparent size (V)	2.1′ × 1.3′
Other designations
	Arp 224, UGC 6823, MGC+09-20-009, PGC 37063

NGC 3921 is an interacting galaxy in the northern constellation of Ursa Major. Estimates using redshift put it at about 59 million light years (18 megaparsecs) from Earth.^[3] It was discovered on 14 April 1789 by William Herschel,^[6] and was described as "pretty faint, small, round" by John Louis Emil Dreyer, the compiler of the New General Catalogue.^[7]

NGC 3921 is the remnant of a galaxy merger. The two progenitor galaxies are thought to have been disk galaxies that collided about 700 million years ago.^[8] The image shows noticeable star formation and structures like loops, indicative of galaxies interacting.^[8] Because of this, NGC 3921 was included in Halton Arp's Atlas of Peculiar Galaxies under the designation Arp 224.^[4]

Being a starburst galaxy, NGC 3921 has important features. One of them is an ultraluminous X-ray source, designated X-2, with an X-ray luminosity of 8×10³⁹ erg/s.^[9] Additionally, two candidate globular clusters have been detected within NGC 3921.^[5] They are both fairly young, and about half as massive as Omega Centauri, demonstrating that mergers of gas-rich galaxies can also create more metal-rich globular clusters.^[5]

References

^ ^a ^b Skrutskie, Michael F.; Cutri, Roc M.; Stiening, Rae; Weinberg, Martin D.; Schneider, Stephen E.; Carpenter, John M.; Beichman, Charles A.; Capps, Richard W.; Chester, Thomas; Elias, Jonathan H.; Huchra, John P.; Liebert, James W.; Lonsdale, Carol J.; Monet, David G.; Price, Stephan; Seitzer, Patrick; Jarrett, Thomas H.; Kirkpatrick, J. Davy; Gizis, John E.; Howard, Elizabeth V.; Evans, Tracey E.; Fowler, John W.; Fullmer, Linda; Hurt, Robert L.; Light, Robert M.; Kopan, Eugene L.; Marsh, Kenneth A.; McCallon, Howard L.; Tam, Robert; Van Dyk, Schuyler D.; Wheelock, Sherry L. (1 February 2006). "The Two Micron All Sky Survey (2MASS)". The Astronomical Journal. 131 (2): 1163–1183. Bibcode:2006AJ....131.1163S. doi:10.1086/498708. ISSN 0004-6256. S2CID 18913331.
^ ^a ^b ^c ^d "NED results for object NGC 3921". National Aeronautics and Space Administration / Infrared Processing and Analysis Center. Retrieved 28 May 2017.
^ ^a ^b Crook, Aidan C.; Huchra, John P.; Martimbeau, Nathalie; Masters, Karen L.; Jarrett, Tom; Macri, Lucas M. (2007). "Groups of Galaxies in the Two Micron All Sky Redshift Survey". The Astrophysical Journal. 655 (2): 790–813. arXiv:astro-ph/0610732. Bibcode:2007ApJ...655..790C. doi:10.1086/510201. S2CID 11672751.
^ ^a ^b ^c "NGC 3921". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 28 May 2017.
^ ^a ^b ^c Schweizer, François; Seitzer, Patrick; Brodie, Jean P. (2004). "Keck Spectroscopy of Two Young Globular Clusters in the Merger Remnant NGC 3921". The Astronomical Journal. 128 (1): 202–210. arXiv:astro-ph/0404424. Bibcode:2004AJ....128..202S. doi:10.1086/421851. S2CID 14568163.
^ Seligman, Courtney. "New General Catalogue objects: NGC 3900 - 3949". cseligman.com. Retrieved 28 May 2017.
^ "Revised NGC Data for NGC 3921 - Hartmut Frommert - SEDS". seds.org. Retrieved 28 May 2017.
^ ^a ^b "Evolution in slow motion | ESA/Hubble". www.spacetelescope.org. 2015. Retrieved 28 May 2017.
^ Jonker, P. G.; Heida, M.; Torres, M. A. P.; Miller-Jones, J. C. A.; Fabian, A. C.; Ratti, E. M.; Miniutti, G.; Walton, D. J.; Roberts, T. P. (2012). "The Nature of the Bright Ulx X-2 in Ngc 3921: Achandraposition Andhstcandidate Counterpart". The Astrophysical Journal. 758 (1): 28. arXiv:1208.4502. Bibcode:2012ApJ...758...28J. doi:10.1088/0004-637X/758/1/28. S2CID 59330131.