速度離散
外觀
在天文學中,速度離散(「σ」)是一群天體(如疏散星團、球狀星團、星系、星系團或超星系團)速度的離散程度。使用天體光譜學測量天體成員的視向速度可以測量出天體的速度離散,再由維里定理得到天體的質量。[1]通過測量天體譜線的多普勒致寬效應得到視線速度。天體的視向速度測量得越多,其離散程度就越精確。中心速度離散指的是分散的天體(如星系或星系團)內部區域σ的離散程度。
在天文學中,天體的速度離散和物質(或由物質噴射的電磁輻射)之間的關係能以數種形式表達。例如,M-σ關係用於圍繞黑洞的物質質量計算,法貝爾-傑克遜關係用於橢圓星系。銀河系超大質量黑洞的σ值約為75km/h。[2]仙女座星系(M31)的超大質量黑洞比銀河系超大質量黑洞大10倍,它的σ值約為160km/s。[2]
星系群核星系團的速度離散範圍比小天體更寬。例如,我們所處的「貧」星系群——本星系群的σ值為61±8km/s。[3]但「富」星系群,如后髮座星系團,其σ值約為1000km/s。[4]特別地,后髮座星系群的矮橢圓星系有它們自己內部恆星的離散速度,σ值約為80km/s。[5]相比之下,普通的橢圓星系的σ值約為200km/s。[6]
對於漩渦星系來說,第一星族恆星的速度離散增長是一種漸進過程,多半是由隨機的動量改變導致的,這種動量改變被認為是獨立恆星與質量大於或約等於105 M☉的星際塵和星際雲間的動態摩擦產生的。[7]正面漩渦星系的中心速度離散值大於或約等於90km/s,若是側向的漩渦星系,會稍微更大一點。[8]
相關條目
[編輯]外部連結
[編輯]- ^ Collins Dictionary of Astronomy, 2nd Ed.; Harper Collins Publishers; 2000; pp.444,449
- ^ 2.0 2.1 Gebhardt, Karl; Bender, Ralf; Bower, Gary; Dressler, Alan; Faber, S. M.; Filippenko, Alexei V.; Green, Richard; Grillmair, Carl; Ho, Luis C.; Kormendy, John; Lauer, Tod R.; Magorrian, John; Pinkney, Jason; Richstone, Douglas; Tremaine, Scott. A Relationship between Nuclear Black Hole Mass and Galaxy Velocity Dispersion (PDF). The Astrophysical Journal (Chicago, Illinois, USA: The University of Chicago Press). June 2000, 539 (1): L13–L16 [March 10, 2010]. Bibcode:2000ApJ...539L..13G. arXiv:astro-ph/0006289
. doi:10.1086/312840.
- ^ van den Bergh, Sidney. The local group of galaxies. The Astronomy and Astrophysics Review (Springer). 1999, 9 (3-4): 273–318 (1999). Bibcode:1999A&ARv...9..273V. doi:10.1007/s001590050019.
- ^ Struble, Mitchell F.; Rood, Herbert J. A Compilation of Redshifts and Velocity Dispersions for ACO Clusters (PDF). The Astrophysical Journal Supplement Series (Chicago, Illinois, USA: The University of Chicago Press). November 1999, 125 (1): 35–71 [March 10, 2012]. Bibcode:1999ApJS..125...35S. doi:10.1086/313274.
- ^ Kourkchi, E.; Khosroshahi, H. G.; Carter, D.; Karick, A. M.; Mármol-Queraltó, E.; Chiboucas, K.; Tully, R. B.; Mobasher, B.; Guzmán, R.; Matković, A.; Gruel, N. Dwarf galaxies in the Coma cluster – I. Velocity dispersion measurements. Monthly Notices of the Royal Astronomical Society (Wiley Online Library). March 2012, 420 (4): 2819–2834. Bibcode:2012MNRAS.420.2819K. arXiv:1110.2649
. doi:10.1111/j.1365-2966.2011.19899.x.
- ^ Forbes, Duncan A.; Ponman, Trevor J. On the relationship between age and dynamics in elliptical galaxies (PDF). Monthly Notices of the Royal Astronomical Society. November 1999, 309 (3): 623–628 [March 10, 2012]. Bibcode:1999MNRAS.309..623F. arXiv:astro-ph/9906368
. doi:10.1046/j.1365-8711.1999.02868.x. (原始內容 (PDF)存檔於2021-08-31).
- ^ Spitzer, Lyman Jr.; Schwarzschild, Martin. The Possible Influence of Interstellar Clouds on Stellar Velocities. II. (PDF). Astrophysical Journal. July 1953, 118: 106 [March 10, 2012]. Bibcode:1953ApJ...118..106S. doi:10.1086/145730. (原始內容 (PDF)存檔於2021-08-31).
- ^ Bershady, Matthew A.; Martinsson, Thomas P. K.; Verheijen, Marc A. W.; Westfall, Kyle B.; Andersen, David R.; Swaters, Rob A. Galaxy Disks are Submaximal. The Astrophysical Journal Letters. October 2011, 739 (2): L47. Bibcode:2011ApJ...739L..47B. arXiv:1108.4314
. doi:10.1088/2041-8205/739/2/L47.