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]

Contents

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

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, [lower-alpha 1] 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

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

NameDiameter (kpc)Distance
(kpc)		 Absolute visual magnitude Type Discovered
Large Magellanic Cloud 448.5−18.1SBmprehistoric
Antlia 2 2.9130−8.5Irr?2018
Sagittarius Dwarf 2.620−13.5E1994
Crater II 2.2117.5−8.2dSph2016 [8]
Small Magellanic Cloud 261−16.8Irrprehistoric
Canes Venatici I 1.1220−8.6dSph2006
Canis Major Dwarf 1.58−14.4Irr2003
Boötes III 1.046−5.75dSph?2009
Sculptor Dwarf 0.890−11.1dE31937
Draco Dwarf 0.780−8.8dE01954
Hercules 0.7135−6.6dSph2006
Leo II 0.7210−9.8dE01950
Fornax Dwarf 0.6140−13.4dE21938
Eridanus II [9] 0.55366−7.1dSph2015 [10] [11]
Sextans Dwarf Spheroidal 0.590−9.3dE31990
Carina Dwarf Spheroidal 0.5100−9.1dE31977
Leo I 0.5250−12.0dE31950
Ursa Minor Dwarf 0.460−8.8dE41954
Leo T 0.34420−8.0dSph/dIrr2006
Aquarius II 0.32108−4.2dSph2016 [12]
Boötes I 0.3060−6.3dSph2006
Canes Venatici II 0.30155−4.9dSph2006
Leo IV 0.30160−5.8dSph2006
Tucana IV 0.2548−3.5dSph2015 [13]
Columba I 0.21182−4.5dSph2015 [13]
Ursa Major II Dwarf 0.2030−4.25dG D2006
Grus II 0.1953−3.9dSph2015 [13]
Cetus III 0.18251−2.4dSph?2017 [14]
Coma Berenices 0.1442−4.1dSph2006
Hydra II 0.14128−4.8dSph2015 [15]
Reticulum III 0.1392−3.3dSph2015 [13]
Pisces II 0.12180−5.0dSph2010
Pegasus III 0.11215−3.4dSph2015 [16] [17]
Hydrus I 0.1028−4.7dSph2018 [18]
Boötes II 0.1042−2.7dSph2007
Tucana III 0.0925−2.4dSph2015 [13]
Virgo I 0.0991−0.3dSph?2016 [14]
Horologium II 0.0978−2.6dSph2015 [19]
Sagittarius II 0.0867−5.2dSph2015 [20]
Leo V 0.08180−5.2dSph2007
Triangulum II 0.0730−1.8dSph2015
Segue 2 0.0735−2.5dSph2007
Segue 1 0.0623−1.5dSph2007
Draco II 0.0420−2.9dSph2015 [20]
Tucana V 0.0355−1.6dSph2015 [13]
Cetus II 0.03300.0dSph?2015 [13]
Reticulum II 0.06430−3.6dSph2015 [10] [11]
Tucana II 0.3370−3.9dSph2015 [10] [11]
Pisces Overdensity 1.580−13dSph?2009
DES 1 0.0282−3.05GC2016 [21]
Eridanus III 0.02890−2.4dSph? [lower-alpha 2] 2015 [10] [11]
Horologium I 0.06100−3.5dSph? [lower-alpha 2] 2015 [10] [11]
Kim 2/Indus I 0.074100−3.5GC2015 [10] [11]
Phoenix II 0.0521100−3.7dSph? [lower-alpha 2] 2015 [10] [11]
Ursa Major I Dwarf 0.64100−5.5dG D2005
Pictoris I 0.058115−3.7dSph? [lower-alpha 2] 2015 [10] [11]
Grus I 0.12120−3.4dSph2015 [10]
Pegasus IV 0.08290−4.25dSph2022 [22]
Carina II 0.18236−4.5dSph2018 [23]
Carina III 0.0628−2.4GC?2018 [23]
Boötes IV 0.28209−4.53dSph2019 [24]
Centaurus I 0.076116−5.55dSph2020 [25]
Pictor II 0.04646−3.2dSph2016 [26]
Willman 1 0.0238−2.53dSph2018 [27]
Ursa Major III 0.00310+2.2dSph2023

Map with clickable regions

Milky Way's satellite galaxies (clickable map) Satellite Galaxies.svg
Milky Way's satellite galaxies (clickable map)

Streams

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.

See also

Notes

  1. ↑ The distance to edge of the dark matter halo of the galaxy from its center is the virial radius of a galaxy, Rvir
  2. 1 2 3 4 May be a globular cluster instead

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    <span class="mw-page-title-main">Local Group</span> Group of galaxies that includes the Milky Way

    The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly 3 megaparsecs (10 million light-years; 9×1019 kilometres), and a total mass of the order of 2×1012 solar masses (4×1042 kg). It consists of two collections of galaxies in a "dumbbell" shape; the Milky Way and its satellites form one lobe, and the Andromeda Galaxy and its satellites constitute the other. The two collections are separated by about 800 kiloparsecs (3×10^6 ly; 2×1019 km) and are moving toward one another with a velocity of 123 km/s. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster. The exact number of galaxies in the Local Group is unknown as some are occluded by the Milky Way; however, at least 80 members are known, most of which are dwarf galaxies.

    <span class="mw-page-title-main">Dwarf galaxy</span> Small galaxy composed of up to several billion stars

    A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.

    <span class="mw-page-title-main">Dwarf spheroidal galaxy</span> Small, low-luminosity galaxy with an old stellar population and little dust

    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 as 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.

    <span class="mw-page-title-main">Boötes I</span>

    The Boötes Dwarf Galaxy is a galaxy discovered in 2006, which appears faint, with a luminosity of 100,000 L☉ and an absolute magnitude of –5.8. It lies about 197,000 light-years away in the constellation Boötes. This dwarf spheroidal galaxy appears to be tidally disrupted by the Milky Way Galaxy, which it orbits, and has two stellar tails that cross over to form a cross. Tidally disrupted galaxies usually only form one tail. The galaxy appears to be significantly elongated, with an ellipticity of ε = 0.68 ± 0.15.

    Coma Berenices or Com is a dwarf spheroidal galaxy situated in the Coma Berenices constellation and discovered in 2006 in data obtained by the Sloan Digital Sky Survey. The galaxy is located at the distance of about 44 kpc from the Sun and moves away from the Sun with the velocity of about 98 km/s. It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an elliptical shape with the half-light radius of about 70 pc.

    Pisces II is a dwarf spheroidal galaxy situated in the Pisces constellation and discovered in 2010 in the data obtained by the Sloan Digital Sky Survey. The galaxy is located at the distance of about 180 kpc (kiloparsecs) from the Sun. It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an elongated shape with the half-light radius of about 60 pc and ratio of the axis of about 5:3.

    The Pisces Overdensity is a clump of stars in the Milky Way's halo, which may be a disrupted dwarf spheroidal galaxy. It is situated in the Pisces constellation and was discovered in 2009 by analysis of distribution of RR Lyrae stars in the data obtained by the Sloan Digital Sky Survey's data. The galaxy is located at the distance of about 80 kpc from the Sun and moves towards it with a speed of about 75 km/s.

    Galaxy X is a postulated dark satellite dwarf galaxy of the Milky Way Galaxy. If it exists, it would be composed mostly of dark matter and interstellar gas with few stars. Its proposed location is some 90 kpc (290 kly) from the Sun, behind the disk of the Milky Way, and some 12 kpc (39 kly) in extent. Galactic coordinates would be (l= -27.4°,b=-1.08°).

    <span class="mw-page-title-main">Ultra diffuse galaxy</span> Extremely low luminosity galaxy

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    <span class="mw-page-title-main">Laevens 1</span>

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    Reticulum II is a dwarf galaxy in the Local Group. Reticulum II was discovered in 2015 by analysing images from the Dark Energy Survey. It is a satellite of the Magellanic Clouds and was probably captured relatively recently. Like other dwarf spheroidal galaxies, its stellar population is old: the galaxy was quenched before 11.5 billion years ago.

    Crater 2 is a low-surface-brightness dwarf satellite galaxy of the Milky Way, located approximately 380,000 ly from Earth. Its discovery in 2016 revealed significant gaps in astronomers' understanding of galaxies possessing relatively small half-light diameters and suggested the possibility of many undiscovered dwarf galaxies orbiting the Milky Way. Crater 2 was identified in imaging data from the VST ATLAS survey.

    <span class="mw-page-title-main">Dragonfly 44</span> Galaxy in constellation Coma Berenices

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    The Eridanus II Dwarf is a low-surface brightness dwarf galaxy in the constellation Eridanus. Eridanus II was independently discovered by two groups in 2015, using data from the Dark Energy Survey. This galaxy is probably a distant satellite of the Milky Way. Eridanus II contains a centrally located globular cluster; and is the smallest, least luminous galaxy known to contain a globular cluster. Crnojević et al., 2016. Eridanus II is significant, in a general sense, because the widely accepted Lambda CDM cosmology predicts the existence of many more dwarf galaxies than have yet been observed. The search for just such bodies was one of the motivations for the ongoing Dark Energy Survey observations. Eridanus II has special significance because of its apparently stable globular cluster. The stability of this cluster, near the center of such a small, diffuse, galaxy places constraints on the nature of dark matter.

    <span class="mw-page-title-main">Gaia Sausage</span> Remains galaxy merger in the Milky Way

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    <span class="mw-page-title-main">Antlia II</span> Low surface-brightness dwarf satellite galaxy of the Milky Way

    Antlia II is a low-surface-brightness dwarf satellite galaxy of the Milky Way at a galactic latitude of 11.2°. It spans 1.26° in the sky just southeast of Epsilon Antliae. The galaxy is similar in size to the Large Magellanic Cloud, despite being 1/10,000 as bright. Antlia II has the lowest surface brightness of any galaxy discovered and is ~ 100 times more diffuse than any known ultra diffuse galaxy. The large size of the galaxy suggests that it is currently being tidally disrupted, and is in the process of becoming a stellar stream. The southeast side of Antlia II is farther away than the northwest side, likely due to the tidal disruption. It was discovered using data from the European Space Agency's Gaia spacecraft in November 2018.

    References

    1. ↑ 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.
    2. 1 2 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.
    3. ↑ "Press release: Magellanic Clouds May Be Just Passing Through". Harvard University. January 9, 2007.
    4. ↑ 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 .
    5. ↑ "Milky Way Ransacks Nearby Dwarf Galaxies". SpaceDaily. 17 October 2014.
    6. ↑ "Milky Way ransacks nearby dwarf galaxies". ScienceDaily. 15 October 2014.
    7. ↑ Sjölander, Nils. "Milky Way satellite galaxies". Archived from the original on 2014-02-19.
    8. ↑ 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.
    9. ↑ 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.
    10. 1 2 3 4 5 6 7 8 9 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.
    11. 1 2 3 4 5 6 7 8 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.
    12. ↑ 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.
    13. 1 2 3 4 5 6 7 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.
    14. 1 2 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.
    15. ↑ 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.
    16. ↑ 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.
    17. ↑ 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.
    18. ↑ 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.
    19. ↑ 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.
    20. 1 2 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.
    21. ↑ 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.
    22. ↑ 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.
    23. 1 2 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.
    24. ↑ 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.
    25. ↑ 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.
    26. ↑ 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.
    27. ↑ 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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