NGC 4921

NGC 4921
NGC 4921 in a combination of near-infrared and yellow light.
Observation data (J2000 epoch)
Constellation	Coma Berenices
Right ascension	12h 59m 01.596s[1]
Declination	+28° 09′ 17.27″[1]
Redshift	0.018286; 5,482 km/s[2]
Distance	ca. 320 Mly[3]
Type	SB(rs)ab[1]
Apparent dimensions (V)	2.5′ × 2.2′[1]
Apparent magnitude (V)	13.04[1]
Other designations
NGC 4921, UGC 08134, PGC 044899.[1]
See also: Galaxy, List of galaxies

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]

In 1976, 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, which means it is low in non-ionized hydrogen gas. The distribution of the gas 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.^[7]

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,^[8] and reached an estimated peak magnitude of 18.5.^[9] The light curve proved similar to supernova SN 1987a in the Large Magellanic Cloud,^[10] and it displayed "unusual photometric behavior".^[8]

References

1. ^ ^{a b c d e f} "NASA/IPAC Extragalactic Database". Results for NGC 4921. http://nedwww.ipac.caltech.edu/. 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. ^ ^{a b} Atkinson, Nancy (2009-02-05). "Deep Hubble View of Unusual "Fluffy" Galaxy – and Beyond". Universe Today. http://www.universetoday.com/2009/02/05/deep-hubble-view-of-unusual-fluffy-galaxy-–-and-beyond/. Retrieved 2009-02-05. ^{[dead link]}
4. ^ Christensen, Lars Lindberg (2009-02-05). "Exceptionally deep view of strange galaxy". European Space Agency. http://www.esa.int/esaSC/SEMA1NXPXPF_index_0.html. 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; Mobasher, Bahram; Okamura, S.; Kashikawa, N. (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. 
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. 
8. ^ ^{a b} Barbon, R. (January 1978). "Supernovae in the Coma cluster of galaxies". Astronomical Journal 83: 13–19. Bibcode 1978AJ.....83...13B. doi:10.1086/112170. 
9. ^ 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. 
10. ^ "The supernova 1959b in NGC 4921" (in Russian). Astrofizika 27: 609–612. 12/1987. Bibcode 1987Afz....27..609S.