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Dwarf spheroidal galaxy

December 15, 2023

A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low-luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and to systems that are companions to the Andromeda Galaxy (M31). While similar to dwarf elliptical galaxies in appearance and properties such as little to no gas or dust or recent star formation, they are approximately spheroidal in shape and generally have lower luminosity.

NGC147 (left) and the Fornax Dwarf (right), two of the earliest known dwarf spheroidal galaxies.

Discovery edit

Despite the radii of dSphs being much larger than those of globular clusters, they are much more difficult to find due to their low luminosities and surface brightnesses. Dwarf spheroidal galaxies have a large range of luminosities, and known dwarf spheroidal galaxies span several orders of magnitude of luminosity.[1] Their luminosities are so low that Ursa Minor, Carina, and Draco, the known dwarf spheroidal galaxies with the lowest luminosities, have mass-to-light ratios (M/L) greater than that of the Milky Way.[2] Dwarf spheroidals also have little to no gas with no obvious signs of recent star formation.[3][4] Within the Local Group, dSphs are primarily found near the Milky Way and M31.[5][6]

The first dwarf spheroidal galaxies discovered were Sculptor and Fornax in 1938.[2] The Sloan Digital Sky Survey has resulted in the discovery of 11 more dSph galaxies as of 2007[7] By 2015, many more ultra-faint dSphs were discovered, all satellites of the Milky Way.[8] Nine potentially new dSphs were discovered in the Dark Energy Survey in 2015.[9] Each dSph is named after constellations they are discovered in, such as the Sagittarius dwarf spheroidal galaxy, all of which consist of stars generally much older than 1–2 Gyr that formed over the span of many gigayears.[2]

For example, 98% of the stars in the Carina dwarf spheroidal galaxy are older than 2 Gyr, formed over the course of three bursts around 3, 7 and 13 Gyr ago.[2] The stars in Carina have also been found to be metal-poor.[10] This is unlike star clusters because, while star clusters have stars which formed more or less the same time, dwarf spheroidal galaxies experience multiple bursts of star formation.[2]

Evidence of dark matter edit

Because of the faintness of the lowest-luminosity dwarf spheroidal galaxies and the nature of the stars contained within them, some astronomers suggest that dwarf spheroidal galaxies and globular clusters may not be clearly separate and distinct types of objects.[11] Other recent studies, however, have found a distinction in that the total amount of mass inferred from the motions of stars in dwarf spheroidals is many times that which can be accounted for by the mass of the stars themselves. Studies reveal that dwarf spheroidal galaxies have a dynamical mass of around 107 M☉, which is very large despite the low luminosity of dSph galaxies.[1]

Although at fainter luminosities of dwarf spheroidal galaxies, it is not universally agreed upon how to differentiate between a dwarf spheroidal galaxy and a star cluster; however, many astronomers decide this depending on the object's dynamics: If it seems to have more dark matter, then it is likely that it is a dwarf spheroidal galaxy rather than an enormous, faint star cluster. In the current predominantly accepted Lambda cold dark matter cosmological model, the presence of dark matter is often cited as a reason to classify dwarf spheroidal galaxies as a different class of object from globular clusters, which show little to no signs of dark matter. Because of the extremely large amounts of dark matter in dwarf spheroidal galaxies, they may deserve the title "most dark matter-dominated galaxies."[12]

Further evidence of the prevalence of dark matter in dSphs includes the case of Fornax dwarf spheroidal galaxy, which can be assumed to be in dynamic equilibrium to estimate mass and amount of dark matter, since the gravitational effects of the Milky Way are small.[13] Unlike the Fornax galaxy, there is evidence that the UMa2, a dwarf spheroidal galaxy in the Ursa Major constellation, experiences strong tidal disturbances from the Milky Way.[9]

A topic of research is how much the internal dynamics of dwarf spheroidal galaxies are affected by the gravitational tidal dynamics of the galaxy they are orbiting. In other words, dwarf spheroidal galaxies could be prevented from achieving equilibrium due to the gravitational field of the Milky Way or other galaxy that they orbit.[2] For example, the Sextans dwarf spheroidal galaxy has a velocity dispersion of 7.9±1.3 km/s, which is a velocity dispersion that could not be explained solely by its stellar mass according to the Virial Theorem. Similar to Sextans, previous studies of Hercules dwarf spheroidal galaxy reveal that its orbital path does not correspond to the mass contained in Hercules.[14] Furthermore, there is evidence that the UMa2, a dwarf spheroidal galaxy in the Ursa Major constellation, experiences strong tidal disturbances from the Milky Way.[9]

References edit

  1. ^ a b Strigari, Louis E.; Bullock, James S.; Kaplinghat, Manoj; Simon, Joshua D.; Geha, Marla; Willman, Beth; Walker, Matthew G. (2008-08-28). "A common mass scale for satellite galaxies of the Milky Way". Nature. 454 (7208): 1096–1097. arXiv:0808.3772. Bibcode:2008Natur.454.1096S. doi:10.1038/nature07222. ISSN 0028-0836. PMID 18756252. S2CID 4373541.
  2. ^ a b c d e f Sparke, L.S.; Gallagher, J.S. III (2016). Galaxies in the Universe. United Kingdom: Cambridge University Press. pp. 162–165. ISBN 978-0-521-67186-6.
  3. ^ Ferguson, Henry C.; Binggeli, Bruno (1994). "NASA/ADS Search". Astronomy and Astrophysics Review. 6 (1–2): 67. arXiv:astro-ph/9409079. Bibcode:1994A&ARv...6...67F. doi:10.1007/BF01208252. S2CID 18879556.
  4. ^ McConnachie, Alan W. (2012-06-05). "The Observed Properties of Dwarf Galaxies in and Around the Local Group". The Astronomical Journal. 144 (1): 4. arXiv:1204.1562. Bibcode:2012AJ....144....4M. doi:10.1088/0004-6256/144/1/4. ISSN 0004-6256. S2CID 118515618.
  5. ^ Mateo, Mario L. (1998). "NASA/ADS Search". Annual Review of Astronomy and Astrophysics. 36: 435–506. arXiv:astro-ph/9810070. Bibcode:1998ARA&A..36..435M. doi:10.1146/annurev.astro.36.1.435. S2CID 119333888.
  6. ^ K., Grebel, E. (1998). "Star Formation Histories of Local Group Dwarf Galaxies". Highlights of Astronomy. 11: 125–126. arXiv:astro-ph/9806191. Bibcode:1998HiA....11..125G. doi:10.1017/S1539299600020190.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ Simon, Josh; Geha, Marla (November 2007). "The kinematics of the ultra-faint Milky Way satellites: Solving the missing satellite problem". The Astrophysical Journal. 670 (1): 313–331. arXiv:0706.0516. Bibcode:2007ApJ...670..313S. doi:10.1086/521816. S2CID 9715950.
  8. ^ Koposov, Sergey E.; Belokurov, Vasily; Torrealba, Gabriel; Evans, N. Wyn (10 March 2015). "Beasts of the southern wild: Discovery of a large number of ultra-faint satellites in the vicinity of the Magellanic clouds". The Astrophysical Journal. 805 (2): 130. arXiv:1503.02079. Bibcode:2015ApJ...805..130K. doi:10.1088/0004-637X/805/2/130. S2CID 118267222.
  9. ^ a b c Bonnivard, V.; Combet, C.; Daniel, M.; Funk, S.; Geringer-Sameth, A.; Hinton, J.A.; et al. (2015). "Dark matter annihilation and decay in dwarf spheroidal galaxies: The classical and ultrafaint dSphs". Monthly Notices of the Royal Astronomical Society. 453 (1): 849–867. arXiv:1504.02048. Bibcode:2015MNRAS.453..849B. doi:10.1093/mnras/stv1601.
  10. ^ Bono, G.; Stetson, P.B.; Walker, A.R.; Monelli, M.; Fabrizio, M.; Pietrinferni, A.; et al. (2010-01-01). "On the stellar content of the Carina dwarf spheroidal galaxy". Publications of the Astronomical Society of the Pacific. 122 (892): 651. arXiv:1004.2559. Bibcode:2010PASP..122..651B. doi:10.1086/653590. ISSN 1538-3873. S2CID 119301603.
  11. ^ van den Bergh, Sidney (November 2007). "Globular clusters and dwarf spheroidal galaxies". Monthly Notices of the Royal Astronomical Society: Letters. 385 (1): L20–L22. arXiv:0711.4795. Bibcode:2008MNRAS.385L..20V. doi:10.1111/j.1745-3933.2008.00424.x. S2CID 15093329.
  12. ^ Strigari, Louie; Koushiappas, Savvas M.; Bullock, James S.; Kaplinghat, Manoj; Simon, Joshua D.; Geha, Marla; Willman, Beth; et al. (2008). "The most dark matter dominated galaxies: Predicted gamma-ray signals from the faintest Milky Way dwarfs". The Astrophysical Journal. 678 (2): 614–620. arXiv:0709.1510. Bibcode:2008ApJ...678..614S. doi:10.1086/529488. S2CID 11415491.
  13. ^ Battaglia, Giuseppina; Sollima, Antonio; Nipoti, Carlo (2015). "The effect of tides on the Fornax dwarf spheroidal galaxy". Monthly Notices of the Royal Astronomical Society. 454 (3): 2401–2415. arXiv:1509.02368. Bibcode:2015MNRAS.454.2401B. doi:10.1093/mnras/stv2096.
  14. ^ Roderick, T.A.; Jerjen, H.; Da Costa, G.S.; Mackey, A.D. (2016). "Structural analysis of the Sextans dwarf spheroidal galaxy". Monthly Notices of the Royal Astronomical Society. 460 (1): 30–43. arXiv:1604.06214. Bibcode:2016MNRAS.460...30R. doi:10.1093/mnras/stw949.

December 15, 2023
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A dwarf spheroidal galaxy dSph is a term in astronomy applied to small low luminosity galaxies with very little dust and an older stellar population They are found in the Local Group as companions to the Milky Way and to systems that are companions to the Andromeda Galaxy M31 While similar to dwarf elliptical galaxies in appearance and properties such as little to no gas or dust or recent star formation they are approximately spheroidal in shape and generally have lower luminosity NGC147 left and the Fornax Dwarf right two of the earliest known dwarf spheroidal galaxies Discovery editDespite the radii of dSphs being much larger than those of globular clusters they are much more difficult to find due to their low luminosities and surface brightnesses Dwarf spheroidal galaxies have a large range of luminosities and known dwarf spheroidal galaxies span several orders of magnitude of luminosity 1 Their luminosities are so low that Ursa Minor Carina and Draco the known dwarf spheroidal galaxies with the lowest luminosities have mass to light ratios M L greater than that of the Milky Way 2 Dwarf spheroidals also have little to no gas with no obvious signs of recent star formation 3 4 Within the Local Group dSphs are primarily found near the Milky Way and M31 5 6 The first dwarf spheroidal galaxies discovered were Sculptor and Fornax in 1938 2 The Sloan Digital Sky Survey has resulted in the discovery of 11 more dSph galaxies as of 2007 7 By 2015 many more ultra faint dSphs were discovered all satellites of the Milky Way 8 Nine potentially new dSphs were discovered in the Dark Energy Survey in 2015 9 Each dSph is named after constellations they are discovered in such as the Sagittarius dwarf spheroidal galaxy all of which consist of stars generally much older than 1 2 Gyr that formed over the span of many gigayears 2 For example 98 of the stars in the Carina dwarf spheroidal galaxy are older than 2 Gyr formed over the course of three bursts around 3 7 and 13 Gyr ago 2 The stars in Carina have also been found to be metal poor 10 This is unlike star clusters because while star clusters have stars which formed more or less the same time dwarf spheroidal galaxies experience multiple bursts of star formation 2 Evidence of dark matter editBecause of the faintness of the lowest luminosity dwarf spheroidal galaxies and the nature of the stars contained within them some astronomers suggest that dwarf spheroidal galaxies and globular clusters may not be clearly separate and distinct types of objects 11 Other recent studies however have found a distinction in that the total amount of mass inferred from the motions of stars in dwarf spheroidals is many times that which can be accounted for by the mass of the stars themselves Studies reveal that dwarf spheroidal galaxies have a dynamical mass of around 107 M which is very large despite the low luminosity of dSph galaxies 1 Although at fainter luminosities of dwarf spheroidal galaxies it is not universally agreed upon how to differentiate between a dwarf spheroidal galaxy and a star cluster however many astronomers decide this depending on the object s dynamics If it seems to have more dark matter then it is likely that it is a dwarf spheroidal galaxy rather than an enormous faint star cluster In the current predominantly accepted Lambda cold dark matter cosmological model the presence of dark matter is often cited as a reason to classify dwarf spheroidal galaxies as a different class of object from globular clusters which show little to no signs of dark matter Because of the extremely large amounts of dark matter in dwarf spheroidal galaxies they may deserve the title most dark matter dominated galaxies 12 Further evidence of the prevalence of dark matter in dSphs includes the case of Fornax dwarf spheroidal galaxy which can be assumed to be in dynamic equilibrium to estimate mass and amount of dark matter since the gravitational effects of the Milky Way are small 13 Unlike the Fornax galaxy there is evidence that the UMa2 a dwarf spheroidal galaxy in the Ursa Major constellation experiences strong tidal disturbances from the Milky Way 9 A topic of research is how much the internal dynamics of dwarf spheroidal galaxies are affected by the gravitational tidal dynamics of the galaxy they are orbiting In other words dwarf spheroidal galaxies could be prevented from achieving equilibrium due to the gravitational field of the Milky Way or other galaxy that they orbit 2 For example the Sextans dwarf spheroidal galaxy has a velocity dispersion of 7 9 1 3 km s which is a velocity dispersion that could not be explained solely by its stellar mass according to the Virial Theorem Similar to Sextans previous studies of Hercules dwarf spheroidal galaxy reveal that its orbital path does not correspond to the mass contained in Hercules 14 Furthermore there is evidence that the UMa2 a dwarf spheroidal galaxy in the Ursa Major constellation experiences strong tidal disturbances from the Milky Way 9 References edit a b Strigari Louis E Bullock James S Kaplinghat Manoj Simon Joshua D Geha Marla Willman Beth Walker Matthew G 2008 08 28 A common mass scale for satellite galaxies of the Milky Way Nature 454 7208 1096 1097 arXiv 0808 3772 Bibcode 2008Natur 454 1096S doi 10 1038 nature07222 ISSN 0028 0836 PMID 18756252 S2CID 4373541 a b c d e f Sparke L S Gallagher J S III 2016 Galaxies in the Universe United Kingdom Cambridge University Press pp 162 165 ISBN 978 0 521 67186 6 Ferguson Henry C Binggeli Bruno 1994 NASA ADS Search Astronomy and Astrophysics Review 6 1 2 67 arXiv astro ph 9409079 Bibcode 1994A amp ARv 6 67F doi 10 1007 BF01208252 S2CID 18879556 McConnachie Alan W 2012 06 05 The Observed Properties of Dwarf Galaxies in and Around the Local Group The Astronomical Journal 144 1 4 arXiv 1204 1562 Bibcode 2012AJ 144 4M doi 10 1088 0004 6256 144 1 4 ISSN 0004 6256 S2CID 118515618 Mateo Mario L 1998 NASA ADS Search Annual Review of Astronomy and Astrophysics 36 435 506 arXiv astro ph 9810070 Bibcode 1998ARA amp A 36 435M doi 10 1146 annurev astro 36 1 435 S2CID 119333888 K Grebel E 1998 Star Formation Histories of Local Group Dwarf Galaxies Highlights of Astronomy 11 125 126 arXiv astro ph 9806191 Bibcode 1998HiA 11 125G doi 10 1017 S1539299600020190 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link Simon Josh Geha Marla November 2007 The kinematics of the ultra faint Milky Way satellites Solving the missing satellite problem The Astrophysical Journal 670 1 313 331 arXiv 0706 0516 Bibcode 2007ApJ 670 313S doi 10 1086 521816 S2CID 9715950 Koposov Sergey E Belokurov Vasily Torrealba Gabriel Evans N Wyn 10 March 2015 Beasts of the southern wild Discovery of a large number of ultra faint satellites in the vicinity of the Magellanic clouds The Astrophysical Journal 805 2 130 arXiv 1503 02079 Bibcode 2015ApJ 805 130K doi 10 1088 0004 637X 805 2 130 S2CID 118267222 a b c Bonnivard V Combet C Daniel M Funk S Geringer Sameth A Hinton J A et al 2015 Dark matter annihilation and decay in dwarf spheroidal galaxies The classical and ultrafaint dSphs Monthly Notices of the Royal Astronomical Society 453 1 849 867 arXiv 1504 02048 Bibcode 2015MNRAS 453 849B doi 10 1093 mnras stv1601 Bono G Stetson P B Walker A R Monelli M Fabrizio M Pietrinferni A et al 2010 01 01 On the stellar content of the Carina dwarf spheroidal galaxy Publications of the Astronomical Society of the Pacific 122 892 651 arXiv 1004 2559 Bibcode 2010PASP 122 651B doi 10 1086 653590 ISSN 1538 3873 S2CID 119301603 van den Bergh Sidney November 2007 Globular clusters and dwarf spheroidal galaxies Monthly Notices of the Royal Astronomical Society Letters 385 1 L20 L22 arXiv 0711 4795 Bibcode 2008MNRAS 385L 20V doi 10 1111 j 1745 3933 2008 00424 x S2CID 15093329 Strigari Louie Koushiappas Savvas M Bullock James S Kaplinghat Manoj Simon Joshua D Geha Marla Willman Beth et al 2008 The most dark matter dominated galaxies Predicted gamma ray signals from the faintest Milky Way dwarfs The Astrophysical Journal 678 2 614 620 arXiv 0709 1510 Bibcode 2008ApJ 678 614S doi 10 1086 529488 S2CID 11415491 Battaglia Giuseppina Sollima Antonio Nipoti Carlo 2015 The effect of tides on the Fornax dwarf spheroidal galaxy Monthly Notices of the Royal Astronomical Society 454 3 2401 2415 arXiv 1509 02368 Bibcode 2015MNRAS 454 2401B doi 10 1093 mnras stv2096 Roderick T A Jerjen H Da Costa G S Mackey A D 2016 Structural analysis of the Sextans dwarf spheroidal galaxy Monthly Notices of the Royal Astronomical Society 460 1 30 43 arXiv 1604 06214 Bibcode 2016MNRAS 460 30R doi 10 1093 mnras stw949 Portals nbsp Stars nbsp Spaceflight nbsp Outer space nbsp Solar System Retrieved from https en wikipedia org w index php title Dwarf spheroidal galaxy amp oldid 1169082447, wikipedia, wiki, book, books, library,

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