NGC 3921

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

NGC 3921
NGC 3921, imaged by the Hubble Space Telescope
Observation data (J2000 epoch)
ConstellationUrsa Major
Right ascension11h 51m 06.863s[1]
Declination+55° 04′ 43.38″[1]
Redshift0.019667[2]
Helio radial velocity5896 km/s[2]
Distance277.9 Mly (85.19 Mpc)[3]
Apparent magnitude (V)12.64[4]
Apparent magnitude (B)13.4[4]
Absolute magnitude (V)−22.09[5]
Characteristics
Type(R')SA0/a(s) pec[2]
Size180,200 ly (55,240 pc)[2][note 1]
Apparent size (V)2.1′ × 1.3′
Other designations
Arp 224, UGC 6823, MGC+09-20-009, PGC 37063

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 candidates globular clusters have been detected within NGC 3921.[5] They are both fairly young, and are about half as massive as Omega Centauri: this demonstrates that mergers of gas-rich galaxies can also create more metal-rich globular clusters.[5]

References
  1. Skrutskie, M. (2006). "The Two Micron All Sky Survey (2MASS)". The Astronomical Journal. 131 (2): 1163–1183. Bibcode:2006AJ....131.1163S. doi:10.1086/498708.
  2. "NED results for object NGC 3921". National Aeronautics and Space Administration / Infrared Processing and Analysis Center. Retrieved 28 May 2017.
  3. 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.
  4. "NGC 3921". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 28 May 2017.
  5. 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.
  6. Seligman, Courtney. "New General Catalogue objects: NGC 3900 - 3949". cseligman.com. Retrieved 28 May 2017.
  7. "Revised NGC Data for NGC 3921 - Hartmut Frommert - SEDS". seds.org. Retrieved 28 May 2017.
  8. "Evolution in slow motion | ESA/Hubble". www.spacetelescope.org. 2015. Retrieved 28 May 2017.
  9. 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.

Notes
  1. POSS1 103a-O values used.
  • Media related to NGC 3921 at Wikimedia Commons
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