NGC 3646

NGC 3646 is a galaxy in the Leo constellation that has variously been described as "a strange spiral galaxy" of morphological classication Sc[1] or SAa,[2] or as "a ring-shaped galaxy".[3][4]

NGC 3646
NGC 3646 in the Sloan Digital Sky Survey
Observation data
ConstellationLeo
Right ascension11h 21m 43s
Declination+20° 10′ 10″
Redshift0.01416 +/- 0.00001
Apparent magnitude (V)11.13
Apparent magnitude (B)11.78

NGC 3646 has a structure consisting of three parts: an inner hub, a rapidly rotating spiral, and an irregular outer ring surrounding the spiral with an angular feature at one point of the ring.[3] Although estimates vary for its distance,[3][2] the NASA/IPAC Extragalactic Database lists its distance as 67.49 megaparsecs (220.1 Mly), ±4.74 megaparsecs (15.5 Mly).[4]

Burbidge et al. estimated that their measurements of motion in the outer ring were not consistent with stable circular orbits.[1] Afanas'ev et al. argue that this conclusion was erroneous, based on incorrect measurements. Instead, they find a galaxy rotation curve that "places the galaxy among the most rapidly rotating and massive systems",[3] "one of the largest and most luminous spirals in the local universe".[2]

NGC 3649 from the Sloan Digital Sky Survey

NGC 3646 forms an isolated pair with a smaller companion galaxy, NGC 3649.[3] The high rate of star formation in NGC 3646, the low rate in its companion, and the unusual shape of the outer ring in NGC 3646 may have resulted from interactions between these two galaxies.[2]

Two supernovae have been seen in NGC 3646: SN 1989N,[5][6][7] and SN 1999cd.[8][9]

References
  1. Burbidge, E. Margaret; Burbidge, G. R.; Prendergast, K. H. (1961), "Motions in NGC 3646, a strange spiral galaxy", Astrophysical Journal, 134: 237–243, Bibcode:1961ApJ...134..237B
  2. Smith, Beverly J.; Zaragoza-Cardiel, Javier; Struck, Curtis; Olmsted, Susan; Jones, Keith (February 2016), "A comparative study of knots of star formation in interacting versus spiral galaxies", The Astronomical Journal, 151 (3): 63, arXiv:1601.02664, Bibcode:2016AJ....151...63S, doi:10.3847/0004-6256/151/3/63
  3. Afanas'ev, A. V.; Burenkov, A. N.; Zasov, A. V.; Sil'chenko, O. K. (December 1991), "The rotation of inner parts of spiral galaxies, NGC 497, 895, 972 and 3646.", Astronomicheskii Zhurnal, 68: 1134–1149, Bibcode:1991AZh....68.1134A
  4. "Results for object NGC 3646", NASA/IPAC Extragalactic Database, retrieved 2023-07-29
  5. Mikolajczak, C.; Helin, E.; Roman, B.; Mejia, A. (August 1989), "Supernova 1989N in NGC 3646", IAU Circular, 4823: 2, Bibcode:1989IAUC.4823....2M
  6. Lopez, R.; Riera, A.; Cepa, J. (December 1989), "Supernova 1989N in NGC 3646", IAU Circular, 4932: 2, Bibcode:1989IAUC.4932....2L
  7. Johnson, Greg (18 August 1989), "Sophomore finds a bright spot in astronomy study", Los Angeles Times, retrieved 2023-07-27
  8. Garnavich, P.; Jha, S.; Kirshner, R.; Challis, P.; Berlind, P. (May 1999), "Supernova 1999cd in NGC 3646", IAU Circular, 7172: 1, Bibcode:1999IAUC.7172....1G
  9. Patat, F.; Rizzi, L.; Guzzo, L.; Guerrero, G. (May 1999), "Supernova 1999cd in NGC 3646", IAU Circular, 7172: 2, Bibcode:1999IAUC.7172....1G
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