| 词条 | NGC 4921 |
| 释义 |
| name = NGC 4921 | image = NGC 4921 by HST.jpg | image_size = 320px |caption= NGC 4921 in a combination of near-infrared and yellow light | epoch = J2000 | type = SB(rs)ab[1] | ra = {{RA|13|01|26.1}}[1] 209453.02 | dec = {{DEC|+27|53|09}}[1] | dist_ly = ca. 320 Mly[4] | z = 0.018286; 5,482 km/s[2] | constellation name = Coma Berenices | appmag_v = 13.04[1] |size=~{{convert|64.21|kpc|ly|abbr=on|lk=on|order=flip}} (estimated)[1] | size_v = 2.5′ × 2.2′[1] | names = UGC 08134, PGC 044899.[1] }} 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, indicating 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.[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] References1. ^1 2 3 4 5 6 {{cite web | title=NASA/IPAC Extragalactic Database | work=Results for NGC 4921 | url=http://nedwww.ipac.caltech.edu/ | accessdate=2009-03-05 }} {{Ngc50}}2. ^{{cite journal | author=Haynes, Martha P. | display-authors=etal | title=21 CM H1 Line Spectra of Galaxies in Nearby Clusters | journal=Astronomical Journal | volume=113 | pages=1197–1211 |date=April 1997 | doi=10.1086/118337 | bibcode=1997AJ....113.1197H}} 3. ^1 {{cite web|url=http://www.universetoday.com/2009/02/05/deep-hubble-view-of-unusual-fluffy-galaxy-–-and-beyond/ |title=Deep Hubble View of Unusual "Fluffy" Galaxy – and Beyond |last=Atkinson |first=Nancy |date=2009-02-05 |publisher=Universe Today |accessdate=2009-02-05 }}{{dead link|date=February 2018|bot=medic}}{{cbignore|bot=medic}} 4. ^{{cite web | first=Lars Lindberg | last=Christensen | title=Exceptionally deep view of strange galaxy | date=2009-02-05 | publisher=European Space Agency | url=http://www.esa.int/esaSC/SEMA1NXPXPF_index_0.html | accessdate=2009-02-12 }} 5. ^{{cite journal | author=van den Bergh, S. | title=A new classification system for galaxies | journal=Astrophysical Journal | volume=206 | date=1976-06-15 | pages=883–887 | doi=10.1086/154452| bibcode=1976ApJ...206..883V}} 6. ^{{cite journal | author=Poggianti, Bianca M. | display-authors=4 | author2=Bridges, Terry J. | author3=Komiyama, Y. Yagi, M. | author4=Carter, Dave | author5=Mobasher, Bahram | author6=Okamura, S. | author7=Kashikawa, N. | title=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 | journal=The Astrophysical Journal | volume=601 | issue=1 | pages=197–213 | date=2004-01-20 | doi=10.1086/380195 | bibcode=2004ApJ...601..197P|arxiv = astro-ph/0309449 }} 7. ^{{cite journal | author=Bravo-Alfaro, H. | author2=Cayatte, V. | author3=van Gorkom, J. H. | author4=Balkowski, C. | title=VLA HI Imaging of the brightest spiral galaxies in Coma. | journal=The Astronomical Journal | volume=119 | issue=2 | pages=580–592 |date=February 2000 | doi=10.1086/301194 | bibcode=2000AJ....119..580B|arxiv = astro-ph/9912405 }} 8. ^1 {{cite journal | author=Barbon, R. | title=Supernovae in the Coma cluster of galaxies | journal=Astronomical Journal | volume=83 |date=January 1978 | pages=13–19 | doi=10.1086/112170 | bibcode=1978AJ.....83...13B}} 9. ^{{cite journal | author=Humason, M. L. | author2=Gates, H. S. | title=The 1959 Palomar Supernova Search | journal=Publications of the Astronomical Society of the Pacific | volume=72 | issue=426 | page=208 |date=June 1960 | doi=10.1086/127513 | bibcode=1960PASP...72..208H}} 10. ^{{cite journal | last1=Shakhbazian | first1=R. K. | language=Russian | title=The supernova 1959b in NGC 4921 | journal=Astrofizika | volume=27 | date=December 1987 | pages=609–612 | bibcode=1987Afz....27..609S }} 6 : NGC objects|Barred spiral galaxies|Coma Berenices (constellation)|Coma Cluster|Principal Galaxies Catalogue objects|UGC objects |
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