NGC 4921

NGC 4921
NGC 4921
	哈伯太空望遠鏡拍攝NGC 4921的近紅外線和黃色光波段合成影像
觀測資料（J2000 曆元）
星座	后髮座
赤經	13h 01m 26.1s
赤緯	+27° 53′ 09″
紅移	0.018286; 5,482 km/s
距離	ca. 320 Mly
視星等 (V)	13.04
特徵
類型	SB(rs)ab
角直徑 (V)	2.5′ × 2.2′
其他名稱
	NGC 4921, UGC 08134, PGC 044899.
	參見：星系、星系列表

NGC 4921是一個后髮座星系團內的棒旋星系，位於后髮座，距離地球約3.2億光年^[3]這個星系有一個帶有棒狀結構的核心，周圍由含有新形成的高溫藍色恆星的明顯塵埃環環繞。它的外部則是不尋常地平滑，且欠缺明顯的螺旋臂結構^[4]。

觀測

1976年加拿大籍荷蘭天文學家西德尼·范德胡斯特因為NGC 4921的低恆星形成率，將它歸類為「蒼白星系」。他對該星系的紀錄是「一個極低表面亮度，並且螺旋臂結構分散的星系」。儘管如此，它是后髮座星系團內最明亮的螺旋星系^[5]。NGC 4921位於星系團中心附近，因此相對於星系團平均速度而言有高相對速度（7,560 km/s）^[6]。21公分線的觀測結果顯示它的內部缺少 H I 區域，代表它的中性未電離氫含量並不高。星系內的氣體分布在往東南螺旋臂的方向部分被高度擾動，並且延伸量少於星系的可見光盤面。這可能是從星系被剝離的氣體和星系際介質交互作用的結果^[7]。

1959年5月4日，米爾頓·赫馬森在帕洛馬山天文台以施密特望遠鏡在NGC 4921內發現一顆超新星SN1959B。該顆超新星位置看起來距離星系中心相當遠^[8]，亮度最高達到視星等18.5等^[9]，光變曲線相當類似後來在大麥哲倫星系的SN 1987A^[10]，兩者都有不尋常的測光狀態^[8]。

參考資料

^ ^1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 NASA/IPAC Extragalactic Database. Results for NGC 4921. [2009-03-05]. （原始內容存檔於2011-05-14）.
^ Haynes, Martha P.; et al. 21 CM H1 Line Spectra of Galaxies in Nearby Clusters. Astronomical Journal. April 1997, 113: 1197–1211. Bibcode:1997AJ....113.1197H. doi:10.1086/118337.
^ ^3.0 ^3.1 Atkinson, Nancy. Deep Hubble View of Unusual "Fluffy" Galaxy – and Beyond. Universe Today. 2009-02-05 [2009-02-05]. （原始內容存檔於2009-04-12）.
^ Christensen, Lars Lindberg. Exceptionally deep view of strange galaxy. European Space Agency. 2009-02-05 [2009-02-12]. （原始內容存檔於2012-10-18）.
^ van den Bergh, S. A new classification system for galaxies. Astrophysical Journal. 1976-06-15, 206: 883–887. Bibcode:1976ApJ...206..883V. doi:10.1086/154452.
^ Poggianti, Bianca M.; Bridges, Terry J.; Komiyama, Y. Yagi, M.; Carter, Dave; Mobasher, Bahram; Okamura, S.; Kashikawa, N. 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. 2004-01-20, 601 (1): 197–213. Bibcode:2004ApJ...601..197P. arXiv:astro-ph/0309449 . doi:10.1086/380195.
^ Bravo-Alfaro, H.; Cayatte, V.; van Gorkom, J. H.; Balkowski, C. VLA HI Imaging of the brightest spiral galaxies in Coma.. The Astronomical Journal. February 2000, 119 (2): 580–592. Bibcode:2000AJ....119..580B. arXiv:astro-ph/9912405 . doi:10.1086/301194.
^ ^8.0 ^8.1 Barbon, R. Supernovae in the Coma cluster of galaxies. Astronomical Journal. January 1978, 83: 13–19. Bibcode:1978AJ.....83...13B. doi:10.1086/112170.
^ Humason, M. L.; Gates, H. S. The 1959 Palomar Supernova Search. Publications of the Astronomical Society of the Pacific. June 1960, 72 (426): 208. Bibcode:1960PASP...72..208H. doi:10.1086/127513.
^ Shakhbazian, R. K. The supernova 1959b in NGC 4921. Astrofizika. December 1987, 27: 609–612. Bibcode:1987Afz....27..609S （俄語）.

[ned-1] 1.0 ^1.1 ^1.2 ^1.3 ^1.4 ^1.5 NASA/IPAC Extragalactic Database. Results for NGC 4921. [2009-03-05]. （原始內容存檔於2011-05-14）.

[apj113-2] Haynes, Martha P.; et al. 21 CM H1 Line Spectra of Galaxies in Nearby Clusters. Astronomical Journal. April 1997, 113: 1197–1211. Bibcode:1997AJ....113.1197H. doi:10.1086/118337.

[atkinson-3] 3.0 ^3.1 Atkinson, Nancy. Deep Hubble View of Unusual "Fluffy" Galaxy – and Beyond. Universe Today. 2009-02-05 [2009-02-05]. （原始內容存檔於2009-04-12）.

[4] Christensen, Lars Lindberg. Exceptionally deep view of strange galaxy. European Space Agency. 2009-02-05 [2009-02-12]. （原始內容存檔於2012-10-18）.

[5] van den Bergh, S. A new classification system for galaxies. Astrophysical Journal. 1976-06-15, 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. 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. 2004-01-20, 601 (1): 197–213. Bibcode:2004ApJ...601..197P. arXiv:astro-ph/0309449 . doi:10.1086/380195.

[7] Bravo-Alfaro, H.; Cayatte, V.; van Gorkom, J. H.; Balkowski, C. VLA HI Imaging of the brightest spiral galaxies in Coma.. The Astronomical Journal. February 2000, 119 (2): 580–592. Bibcode:2000AJ....119..580B. arXiv:astro-ph/9912405 . doi:10.1086/301194.

[apj83-8] 8.0 ^8.1 Barbon, R. Supernovae in the Coma cluster of galaxies. Astronomical Journal. January 1978, 83: 13–19. Bibcode:1978AJ.....83...13B. doi:10.1086/112170.

[9] Humason, M. L.; Gates, H. S. The 1959 Palomar Supernova Search. Publications of the Astronomical Society of the Pacific. June 1960, 72 (426): 208. Bibcode:1960PASP...72..208H. doi:10.1086/127513.

[10] Shakhbazian, R. K. The supernova 1959b in NGC 4921. Astrofizika. December 1987, 27: 609–612. Bibcode:1987Afz....27..609S （俄語）.

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