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NGC 4921 is a barred spiral galaxy in the Coma Cluster, located in the constellation Coma Berenices. It is about 320 million light-years from Earth.[3] The galaxy has a nucleus with a bar structure that is surrounded by a distinct ring of dust that contains recently formed, hot blue stars. The outer part consists of unusually smooth, poorly distinguished spiral arms.[4]

NGC 4921
NGC 4921 in a combination of near-infrared and yellw light
Observation data (J2000 epoch)
ConstellationComa Berenices
Right ascension13h 01m 26.1s[1] 209453.02
Declination+27° 53′ 09″[1]
Redshift0.018286; 5,482 km/s[2]
Distanceca. 320 Mly[3]
Apparent magnitude (V)13.04[1]
Characteristics
TypeSB(rs)ab[1]
Size~209,400 ly (64.21 kpc) (estimated)[1]
Apparent size (V)2.5′ × 2.2′[1]
Other designations
UGC 08134, PGC 044899.[1]

In 1976, the Canadian astronomer Sidney Van den Bergh categorized this galaxy as "anemic" because of the low rate at which stars are being formed. He noted that it has "an unusually low surface brightness and exhibits remarkably diffuse spiral arms". Nonetheless, it is the brightest spiral galaxy in the Coma Cluster.[5] This galaxy is located near the center of the cluster and has a high relative velocity (7,560 km/s)[6] compared to the mean cluster velocity. When examined at the 21 cm wavelength Hydrogen line, NGC 4921 was found to be strongly H I deficient, indicating that it is low in hydrogen. The distribution of hydrogen has also been deeply perturbed toward the SE spiral arm and is less extended than the optical disk of the galaxy. This may have been caused by interaction with the intergalactic medium, which is stripping off the gas via ram pressure.[7] Some filaments of gas that have been stripped away are falling back to the galaxy, making NGC 4921 possibly the first observational evidence of this fallback.[8]

On May 4, 1959, a supernova explosion was observed in this galaxy by M. L. Humason using a Schmidt telescope at the Palomar Observatory. It appeared "quite far from the center" of the galaxy,[9] and reached an estimated peak magnitude of 18.5.[10] The light curve proved similar to supernova SN 1987a in the Large Magellanic Cloud,[11] and it displayed "unusual photometric behavior".[9]


References


  1. "NASA/IPAC Extragalactic Database". Results for NGC 4921. Retrieved 2009-03-05.
  2. Haynes, Martha P.; et al. (April 1997). "21 CM H1 Line Spectra of Galaxies in Nearby Clusters". Astronomical Journal. 113: 1197–1211. Bibcode:1997AJ....113.1197H. doi:10.1086/118337.
  3. Atkinson, Nancy (2009-02-05). "Deep Hubble View of Unusual "Fluffy" Galaxy – and Beyond". Universe Today. Archived from the original on 2009-02-08. Retrieved 2009-02-05.
  4. Christensen, Lars Lindberg (2009-02-05). "Exceptionally deep view of strange galaxy". European Space Agency. Retrieved 2009-02-12.
  5. van den Bergh, S. (1976-06-15). "A new classification system for galaxies". Astrophysical Journal. 206: 883–887. Bibcode:1976ApJ...206..883V. doi:10.1086/154452.
  6. Poggianti, Bianca M.; Bridges, Terry J.; Komiyama, Y. Yagi, M.; Carter, Dave; et al. (2004-01-20). "A Comparison of the Galaxy Populations in the Coma and Distant Clusters: The Evolution of k+a Galaxies and the Role of the Intracluster Medium". The Astrophysical Journal. 601 (1): 197–213. arXiv:astro-ph/0309449. Bibcode:2004ApJ...601..197P. doi:10.1086/380195. S2CID 17429859.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. Bravo-Alfaro, H.; Cayatte, V.; van Gorkom, J. H.; Balkowski, C. (February 2000). "VLA HI Imaging of the brightest spiral galaxies in Coma". The Astronomical Journal. 119 (2): 580–592. arXiv:astro-ph/9912405. Bibcode:2000AJ....119..580B. doi:10.1086/301194. S2CID 118308523.
  8. Cramer, W. J.; Kenney, J. D. P.; Tonnesen, S.; Smith, R.; Wong, T.; Jáchym, P.; Cortés, J. R.; Cortés, P. C.; Wu, Y.-T. (2021). "Molecular Gas Filaments and Fallback in the Ram Pressure Stripped Coma Spiral NGC 4921". The Astrophysical Journal. 921 (1): 22. arXiv:2107.11731. Bibcode:2021ApJ...921...22C. doi:10.3847/1538-4357/ac1793. S2CID 236428596.
  9. Barbon, R. (January 1978). "Supernovae in the Coma cluster of galaxies". Astronomical Journal. 83: 13–19. Bibcode:1978AJ.....83...13B. doi:10.1086/112170.
  10. Humason, M. L.; Gates, H. S. (June 1960). "The 1959 Palomar Supernova Search". Publications of the Astronomical Society of the Pacific. 72 (426): 208. Bibcode:1960PASP...72..208H. doi:10.1086/127513.
  11. Shakhbazian, R. K. (December 1987). "The supernova 1959b in NGC 4921". Astrofizika (in Russian). 27: 609–612. Bibcode:1987Afz....27..609S.




На других языках

[de] NGC 4921

NGC 4921 ist eine Balken-Spiralgalaxie mit aktivem Galaxienkern vom Hubble-Typ SBab im Sternbild Coma Berenices am Nordsternhimmel. Sie ist schätzungsweise 246 Millionen Lichtjahre von der Milchstraße entfernt und hat einen Durchmesser von etwa 175.000 Lj. Sie ist die hellste Galaxie des Coma-Galaxienhaufens. Im selben Himmelsareal befinden sich u. a. die Galaxien NGC 4911, NGC 4919, NGC 4923, IC 4044.
- [en] NGC 4921

[es] NGC 4921

NGC 4921 es una galaxia espiral barrada situada en la constelación de Coma Berenices, a una distancia de 320 millones de años luz de la Vía Láctea. Es también la galaxia espiral más brillante del Cúmulo de galaxias de Coma, más brillante por ejemplo que la Galaxia de Andrómeda; sin embargo, sólo puede ser vista mediante telescopios de cierta abertura.

[ru] NGC 4921

NGC 4921 (другие обозначения — UGC 8134, MCG 5-31-98, ZWG 160.95, DRCG 27-97, PGC 44899) — спиральная галактика в созвездии Волос Вероники.


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