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(Top) 1 Characteristics 2 List 3 Map with clickable regions 4 Streams 5 See also 6 Notes 7 References 8 Further reading

Satellite galaxies of the Milky Way

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The Milky Way has several smaller galaxies gravitationally bound to it, as part of the Milky Way subgroup, which is part of the local galaxy cluster, the Local Group.^[1]

There are 61 small galaxies confirmed to be within 420 kiloparsecs (1.4 million light-years) of the Milky Way,^[2] but not all of them are necessarily in orbit, and some may themselves be in orbit of other satellite galaxies. The only ones visible to the naked eye are the Large and Small Magellanic Clouds, which have been observed since prehistory. Measurements with the Hubble Space Telescope in 2006 suggest the Magellanic Clouds may be moving too fast to be orbiting the Milky Way.^[3] Of the galaxies confirmed to be in orbit, the largest is the Sagittarius Dwarf Elliptical Galaxy, which has a diameter of 2.6 kiloparsecs (8,500 ly)^[4] or roughly a twentieth that of the Milky Way.

Characteristics[edit]

Satellite galaxies that orbit from 1,000 ly (310 pc) of the edge of the disc of the Milky Way Galaxy to the edge of the dark matter halo of the Milky Way at 980,000 ly (300 kpc) from the center of the galaxy,^[a] are generally depleted in hydrogen gas compared to those that orbit more distantly. This is because of their interactions with the dense hot gas halo of the Milky Way that strip cold gas from the satellites. Satellites beyond that region still retain copious quantities of gas.^[5]^[6]

List[edit]

The Milky Way's satellite galaxies include the following:^[7]^[2]

Name	Diameter (kpc)	Distance (kpc)	Absolute visual magnitude	Type	Discovered
Large Magellanic Cloud	4	48.5	−18.1	SBm	prehistoric
Antlia 2	2.9	130	−8.5	Irr?	2018
Sagittarius Dwarf	2.6	20	−13.5	E	1994
Crater II	2.2	117.5	−8.2	dSph	2016 ^[8]
Small Magellanic Cloud	2	61	−16.8	Irr	prehistoric
Canes Venatici I	1.1	220	−8.6	dSph	2006
Canis Major Dwarf	1.5	8	−14.4	Irr	2003
Boötes III	1.0	46	−5.75	dSph?	2009
Sculptor Dwarf	0.8	90	−11.1	dE3	1937
Draco Dwarf	0.7	80	−8.8	dE0	1954
Hercules	0.7	135	−6.6	dSph	2006
Leo II	0.7	210	−9.8	dE0	1950
Fornax Dwarf	0.6	140	−13.4	dE2	1938
Eridanus II^[9]	0.55	366	−7.1	dSph	2015 ^[10]^[11]
Sextans Dwarf Spheroidal	0.5	90	−9.3	dE3	1990
Carina Dwarf Spheroidal	0.5	100	−9.1	dE3	1977
Leo I	0.5	250	−12.0	dE3	1950
Ursa Minor Dwarf	0.4	60	−8.8	dE4	1954
Leo T	0.34	420	−8.0	dSph/dIrr	2006
Aquarius II	0.32	108	−4.2	dSph	2016 ^[12]
Boötes I	0.30	60	−6.3	dSph	2006
Canes Venatici II	0.30	155	−4.9	dSph	2006
Leo IV	0.30	160	−5.8	dSph	2006
Tucana IV	0.25	48	−3.5	dSph	2015 ^[13]
Columba I	0.21	182	−4.5	dSph	2015 ^[13]
Ursa Major II Dwarf	0.20	30	−4.25	dG D	2006
Grus II	0.19	53	−3.9	dSph	2015 ^[13]
Cetus III	0.18	251	−2.4	dSph?	2017 ^[14]
Coma Berenices	0.14	42	−4.1	dSph	2006
Hydra II	0.14	128	−4.8	dSph	2015 ^[15]
Reticulum III	0.13	92	−3.3	dSph	2015 ^[13]
Pisces II	0.12	180	−5.0	dSph	2010
Pegasus III	0.11	215	−3.4	dSph	2015 ^[16]^[17]
Hydrus I	0.10	28	−4.7	dSph	2018 ^[18]
Boötes II	0.10	42	−2.7	dSph	2007
Tucana III	0.09	25	−2.4	dSph	2015 ^[13]
Virgo I	0.09	91	−0.3	dSph?	2016 ^[14]
Horologium II	0.09	78	−2.6	dSph	2015 ^[19]
Sagittarius II	0.08	67	−5.2	dSph	2015 ^[20]
Leo V	0.08	180	−5.2	dSph	2007
Triangulum II	0.07	30	−1.8	dSph	2015
Segue 2	0.07	35	−2.5	dSph	2007
Segue 1	0.06	23	−1.5	dSph	2007
Draco II	0.04	20	−2.9	dSph	2015 ^[20]
Tucana V	0.03	55	−1.6	dSph	2015 ^[13]
Cetus II	0.03	30	0.0	dSph?	2015 ^[13]
Reticulum II	0.064	30	−3.6	dSph	2015 ^[10]^[11]
Tucana II	0.33	70	−3.9	dSph	2015 ^[10]^[11]
Pisces Overdensity	1.5	80	−13	dSph?	2009
DES 1	0.02	82	−3.05	GC	2016 ^[21]
Eridanus III	0.028	90	−2.4	dSph?^[b]	2015 ^[10]^[11]
Horologium I	0.06	100	−3.5	dSph?^[b]	2015 ^[10]^[11]
Kim 2/Indus I	0.074	100	−3.5	GC	2015 ^[10]^[11]
Phoenix II	0.0521	100	−3.7	dSph?^[b]	2015 ^[10]^[11]
Ursa Major I Dwarf	0.64	100	−5.5	dG D	2005
Pictoris I	0.058	115	−3.7	dSph?^[b]	2015 ^[10]^[11]
Grus I	0.12	120	−3.4	dSph	2015 ^[10]
Pegasus IV	0.082	90	−4.25	dSph	2022 ^[22]
Carina II	0.182	36	−4.5	dSph	2018 ^[23]
Carina III	0.06	28	−2.4	GC?	2018 ^[23]
Boötes IV	0.28	209	−4.53	dSph	2019 ^[24]
Centaurus I	0.076	116	−5.55	dSph	2020 ^[25]
Pictor II	0.046	46	−3.2	dSph	2016 ^[26]
Willman 1	0.02	38	−2.53	dSph	2018 ^[27]
Ursa Major III	0.003	10	+2.2	dSph	2023

Map with clickable regions[edit]

Milky Way's satellite galaxies (clickable map)

Streams[edit]

The Sagittarius Dwarf Spheroidal Galaxy is currently in the process of being consumed by the Milky Way and is expected to pass through it within the next 100 million years. The Sagittarius Stream is a stream of stars in polar orbit around the Milky Way leeched from the Sagittarius Dwarf. The Virgo Stellar Stream is a stream of stars that is believed to have once been an orbiting dwarf galaxy that has been completely distended by the Milky Way's gravity.

Notes[edit]

^ The distance to edge of the dark matter halo of the galaxy from its center is the virial radius of a galaxy, R_vir

^ ^a ^b ^c ^d May be a globular cluster instead

References[edit]

^ David G. Turner (15 August 2013). "An Eclectic View of our Milky Way Galaxy". Canadian Journal of Physics. 92 (9) (published September 2013): 959–963. arXiv:1310.0014. Bibcode:2014CaJPh..92..959T. doi:10.1139/cjp-2013-0429. S2CID 118390693.

^ ^a ^b A. Drlica-Wagner (2020). "The Astrophysical Journal | Milky Way Satellite Census. I. The Observational Selection Function for Milky Way Satellites in DES Y3 and Pan-STARRS DR1". The Astrophysical Journal. 893 (1): 47. doi:10.3847/1538-4357/ab7eb9. hdl:10150/642363. S2CID 208857848.

^ "Press release: Magellanic Clouds May Be Just Passing Through". Harvard University. January 9, 2007.

^ Karachentsev, I. D.; Karachentseva, V. E.; Hutchmeier, W. K.; Makarov, D. I. (2004). "A Catalog of Neighboring Galaxies". The Astronomical Journal. 127 (4): 2031–2068. Bibcode:2004AJ....127.2031K. doi:10.1086/382905.

^ "Milky Way Ransacks Nearby Dwarf Galaxies". SpaceDaily. 17 October 2014.

^ "Milky Way ransacks nearby dwarf galaxies". ScienceDaily. 15 October 2014.

^ Sjölander, Nils. "Milky Way satellite galaxies". Archived from the original on 2014-02-19.

^ Torrealba, G.; Koposov, S.E.; Belokurov, V.; Irwin, M. (13 April 2016). "The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater". Monthly Notices of the Royal Astronomical Society. 459 (3): 2370–2378. arXiv:1601.07178. Bibcode:2016MNRAS.459.2370T. doi:10.1093/mnras/stw733.

^ Crnojević, D.; Sand, D.J.; Zaritsky, D.; Spekkens, K.; Willman, B.; Hargis, J.R. (2016). "Deep imaging of Eridanus II and its lone star cluster". The Astrophysical Journal. 824 (1): L-14. arXiv:1604.08590. Bibcode:2016ApJ...824L..14C. doi:10.3847/2041-8205/824/1/L14. S2CID 2202492.

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ 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 ^d ^e ^f ^g ^h DES Collaboration (10 March 2015). "Eight New Milky Way companions discovered in first-year Dark Energy Survey data". The Astrophysical Journal. 807 (1): 50. arXiv:1503.02584. Bibcode:2015ApJ...807...50B. doi:10.1088/0004-637X/807/1/50. S2CID 12011753.

^ Torrealba, G.; Koposov, S.E.; Belokurov, V.; Irwin, M.; Collins, M.; Spencer, M.; Ibata, R.; Matteo, M.; Bonaca, A.; Jethwa, P. (2016). "At the survey limits: Discovery of the Aquarius 2 dwarf galaxy in the VST ATLAS and the SDSS data". Monthly Notices of the Royal Astronomical Society. 463 (1): 712–722. arXiv:1605.05338. Bibcode:2016MNRAS.463..712T. doi:10.1093/mnras/stw2051.

^ ^a ^b ^c ^d ^e ^f ^g Drlica-Wagner, A.; et al. (4 November 2015). "Eight ultra-faint galaxy candidates discovered in Year Two of the Dark Energy Survey". The Astrophysical Journal. 813 (2): 109. arXiv:1508.03622. Bibcode:2015ApJ...813..109D. doi:10.1088/0004-637X/813/2/109. S2CID 55909299.

^ ^a ^b Homma, Daisuke; Chiba, Masashi; Okamoto, Sakurako; Komiyama, Yutaka; Tanaka, Masayuki; Tanaka, Mikito; Ishigaki, Miho N.; Hayashi, Kohei; Arimoto, Nobuo (2017-04-19). "Searches for New Milky Way Satellites from the First Two Years of Data of the Subaru/Hyper Suprime-Cam Survey: Discovery of Cetus III". Publications of the Astronomical Society of Japan. 70: S18. arXiv:1704.05977. Bibcode:2018PASJ...70S..18H. doi:10.1093/pasj/psx050.

^ Martin, Nicolas F.; et al. (Survey of the Magellanic Stellar History) (23 April 2015). "Hydra II: A faint and compact Milky Way dwarf galaxy found in the survey of the Magellanic stellar history". The Astrophysical Journal Letters. 804 (1): L5. arXiv:1503.06216. Bibcode:2015ApJ...804L...5M. doi:10.1088/2041-8205/804/1/L5. S2CID 7814048.

^ Kim, Dongwon; Jerjen, Helmut; Mackey, Dougal; Da Costa, Gary S.; Milone, Antonino P. (12 May 2015). "A hero's dark horse: Discovery of an ultra-faint Milky Way satellite in Pegasus". The Astrophysical Journal Letters. 804 (2): L-44. arXiv:1503.08268. Bibcode:2015ApJ...804L..44K. doi:10.1088/2041-8205/804/2/L44. S2CID 119302178.

^ Kim, Dongwon; Jerjen, Helmut; Geha, Marla; Chiti, Anirudh; Milone, Antonino P.; Mackey, Dougal; da Costa, Gary; Frebel, Anna; Conn, Blair (2016). "Portrait of a dark horse: Photometric properties and kinematics of the ultra-faint Milky Way satellite Pegasus III". The Astrophysical Journal. 833 (1): 16. arXiv:1608.04934. Bibcode:2016ApJ...833...16K. doi:10.3847/0004-637X/833/1/16. S2CID 73677994.

^ Koposov, Sergey E.; Walker, Matthew G.; Belokurov, Vasily; Casey, Andrew R.; Geringer-Sameth, Alex; Mackey, Dougal; Da Costa, Gary; Erkal, Denis; Jethwa, Prashin (2018-10-01). "Snake in the Clouds: a new nearby dwarf galaxy in the Magellanic bridge*". Monthly Notices of the Royal Astronomical Society. 479 (4): 5343–5361. arXiv:1804.06430. doi:10.1093/mnras/sty1772. ISSN 0035-8711.

^ Kim, Dongwon & Jerjen, Helmut (28 July 2015). "Horologium II: A second ultra-faint Milky Way satellite in the Horologium constellation". The Astrophysical Journal Letters. 808 (2): L-39. arXiv:1505.04948. Bibcode:2015ApJ...808L..39K. doi:10.1088/2041-8205/808/2/L39. S2CID 117190468.

^ ^a ^b Laevens, B.P.M; Martin, N.F.; Bernard, E.J.; Schlafly, E.F.; Sesar, B. (1 November 2015). "Sagittarius II, Draco II and Laevens 3: Three new Milky Way satellites discovered in the PAN-STARRS 1 3π survey". The Astrophysical Journal. 813 (1): 44. arXiv:1507.07564. Bibcode:2015ApJ...813...44L. doi:10.1088/0004-637X/813/1/44. S2CID 54042426.

^ Luque, E.; et al. (9 February 2016). "Digging deeper into Southern skies: A compact Milky Way companion discovered in first-year Dark Energy Survey data". Monthly Notices of the Royal Astronomical Society. 458 (1): 603–612. arXiv:1508.02381. Bibcode:2016MNRAS.458..603L. doi:10.1093/mnras/stw302.

^ Cerny, W.; et al. (2023). "Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-faint Dwarf Galaxy in the Constellation Pegasus". The Astrophysical Journal. 942 (2): 111. arXiv:2203.11788. Bibcode:2023ApJ...942..111C. doi:10.3847/1538-4357/aca1c3. S2CID 247597301.

^ ^a ^b Torrealba, G.; Belokurov, V.; Koposov, S. E.; Bechtol, K.; Drlica-Wagner, A.; Olsen, K. A. G.; Vivas, A. K.; Yanny, B.; Jethwa, P. (22 January 2018). "Discovery of two neighbouring satellites in the Carina constellation with MagLiteS". Monthly Notices of the Royal Astronomical Society. 475 (4): 5085–5097. arXiv:1801.07279. doi:10.1093/mnras/sty170.

^ Homma (2019). "Boötes. IV. A new Milky Way satellite discovered in the Subaru Hyper Suprime-Cam Survey and implications for the missing satellite problem". Publications of the Astronomical Society of Japan. 71 (5). arXiv:1906.07332. doi:10.1093/pasj/psz076.

^ Mau (2020). "Two Ultra-faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey". The Astrophysical Journal. 890 (2): 136. arXiv:1912.03301. Bibcode:2020ApJ...890..136M. doi:10.3847/1538-4357/ab6c67. S2CID 208857609.

^ Drlica-Wagner (2016). "An Ultra-Faint Galaxy Candidate Discovered in Early Data from the Magellanic Satellites Survey". The Astrophysical Journal. 833 (1): L5. arXiv:1609.02148. Bibcode:2016ApJ...833L...5D. doi:10.3847/2041-8205/833/1/L5. hdl:1885/153579. S2CID 56071154.

^ Muñoz (2018). "A MegaCam Survey of Outer Halo Satellites. III. Photometric and Structural Parameters". The Astrophysical Journal. 860 (1): 66. arXiv:1806.06891. Bibcode:2018ApJ...860...66M. doi:10.3847/1538-4357/aac16b. S2CID 118978019.

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