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A '''satellite galaxy''' is a smaller companion galaxy that travels on bound [[orbit]]s within the [[gravitational potential]] of a more massive and [[Luminosity|luminous]] host [[galaxy]] (also known as the primary galaxy).<ref name=":02">{{Cite book|title=Galactic dynamics|last=1950-|first=Binney, James|date=2008|publisher=Princeton University Press|others=Tremaine, Scott, 1950-|isbn=9781400828722|edition=2nd|location=Princeton|oclc=759807562}}</ref> Satellite galaxies and their constituents are bound to their host galaxy, in the same way that [[planet]]s within our own [[Solar System|solar system]] are gravitationally bound to the [[Sun]].<ref>{{cite web|url=http://spaceplace.nasa.gov/satellite-galaxies/en/|title=What Is a Satellite Galaxy?|publisher=NASA Spaceplace|language=English|accessdate=10 April 2016}}</ref> While most satellite galaxies are [[Dwarf galaxy|dwarf galaxies]], satellite galaxies of large [[galaxy cluster]]s can be much more massive.<ref>{{Cite web|url=https://www.cfa.harvard.edu/~lsales/DwarfGalaxies.html|title=Dwarf Galaxies|website=www.cfa.harvard.edu|access-date=2018-06-10}}</ref> |
A '''satellite galaxy''' is a smaller companion galaxy that travels on bound [[orbit]]s within the [[gravitational potential]] of a more massive and [[Luminosity|luminous]] host [[galaxy]] (also known as the primary galaxy).<ref name=":02">{{Cite book|title=Galactic dynamics|last=1950-|first=Binney, James|date=2008|publisher=Princeton University Press|others=Tremaine, Scott, 1950-|isbn=9781400828722|edition=2nd|location=Princeton|oclc=759807562}}</ref> Satellite galaxies and their constituents are bound to their host galaxy, in the same way that [[planet]]s within our own [[Solar System|solar system]] are gravitationally bound to the [[Sun]].<ref>{{cite web|url=http://spaceplace.nasa.gov/satellite-galaxies/en/|title=What Is a Satellite Galaxy?|publisher=NASA Spaceplace|language=English|accessdate=10 April 2016}}</ref> While most satellite galaxies are [[Dwarf galaxy|dwarf galaxies]], satellite galaxies of large [[galaxy cluster]]s can be much more massive.<ref>{{Cite web|url=https://www.cfa.harvard.edu/~lsales/DwarfGalaxies.html|title=Dwarf Galaxies|website=www.cfa.harvard.edu|access-date=2018-06-10}}</ref> |
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== History == |
== History == |
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=== Early 20th century === |
=== Early 20th century === |
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Prior to the 20th century, the notion that galaxies existed beyond our [[Milky Way]] was not well established. In fact, the idea was so controversial at the time that it led to what is now heralded as the "Shapley-Curtis Great Debate" aptly named after the astronomers [[Harlow Shapley]] and [[Heber Doust Curtis]] that debated the nature of "nebulae" and the size of the Milky Way at the [[National Academy of Sciences]] on April 26, 1920. Shapley argued that the Milky Way was the entire universe (spanning over 100,000 [[Light-year|lightyears]] or 30 [[Parsec|kiloparsec]] across) and that all of the observed "nebulae" (currently known as galaxies) resided within this region. On the other hand, Curtis argued that the Milky way was much smaller and that the observed nebulae were in fact galaxies similar to our own Milky Way.<ref name=":2">{{Cite book|title=Galactic astronomy|last=1950-|first=Binney, James|date=1998|publisher=Princeton University Press|others=Merrifield, Michael, 1964-|isbn=978-0691004020|location=Princeton, NJ|oclc=39108765}}</ref> This debate was not settled until late 1923 when the astronomer [[Edwin Hubble]] measured the distance to [[Andromeda Galaxy|M31]] (currently known as the Andromeda galaxy) using [[Cepheid variable|Cepheid Variable]] stars. By measuring the [[Period (physics)|period]] of these stars, Hubble was able to estimate their intrinsic luminosity and upon combining this with their measured [[apparent magnitude]] he estimated a distance of 300 kpc, which was an [[Order of magnitude|order-of-magnitude]] larger than the estimated size of the universe made by Shapley. This measurement verified that not only was the universe much larger than previously expected, but it also demonstrated that the observed nebulae were actually distant galaxies with a wide range of morphologies (see [[Hubble sequence]]).<ref name=":2" /> |
Prior to the 20th century, the notion that galaxies existed beyond our [[Milky Way]] was not well established. In fact, the idea was so controversial at the time that it led to what is now heralded as the "Shapley-Curtis Great Debate" aptly named after the astronomers [[Harlow Shapley]] and [[Heber Doust Curtis]] that debated the nature of "nebulae" and the size of the Milky Way at the [[National Academy of Sciences]] on April 26, 1920. Shapley argued that the Milky Way was the entire universe (spanning over 100,000 [[Light-year|lightyears]] or 30 [[Parsec|kiloparsec]] across) and that all of the observed "nebulae" (currently known as galaxies) resided within this region. On the other hand, Curtis argued that the Milky way was much smaller and that the observed nebulae were in fact galaxies similar to our own Milky Way.<ref name=":2">{{Cite book|title=Galactic astronomy|last=1950-|first=Binney, James|date=1998|publisher=Princeton University Press|others=Merrifield, Michael, 1964-|isbn=978-0691004020|location=Princeton, NJ|oclc=39108765}}</ref> This debate was not settled until late 1923 when the astronomer [[Edwin Hubble]] measured the distance to [[Andromeda Galaxy|M31]] (currently known as the Andromeda galaxy) using [[Cepheid variable|Cepheid Variable]] stars. By measuring the [[Period (physics)|period]] of these stars, Hubble was able to estimate their intrinsic luminosity and upon combining this with their measured [[apparent magnitude]] he estimated a distance of 300 kpc, which was an [[Order of magnitude|order-of-magnitude]] larger than the estimated size of the universe made by Shapley. This measurement verified that not only was the universe much larger than previously expected, but it also demonstrated that the observed nebulae were actually distant galaxies with a wide range of morphologies (see [[Hubble sequence]]).<ref name=":2" /> |
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=== Halo merger rate === |
=== Halo merger rate === |
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Another utility of the EPS formalism is that it can be used to determine the rate at which a halo of initial mass M merges with a halo with mass between M and M+ΔM.<ref name=":1" /> This rate is given by |
Another utility of the EPS formalism is that it can be used to determine the rate at which a halo of initial mass M merges with a halo with mass between M and M+ΔM.<ref name=":1" /> This rate is given by |
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=== Minor mergers and the origins of thick disk components === |
=== Minor mergers and the origins of thick disk components === |
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Observations of edge-on galaxies suggest the universal presence of a [[thin disk]], [[thick disk]] and [[Galactic halo|halo]] component of galaxies. Despite the apparent ubiquity of these components, there is still ongoing research to determine if the thick disk and thin disk are truly distinct components.<ref>{{Cite journal|last=Bovy|first=Jo|last2=Rix|first2=Hans-Walter|last3=Hogg|first3=David W.|date=2012|title=The Milky Way Has No Distinct Thick Disk|url=http://stacks.iop.org/0004-637X/751/i=2/a=131|journal=The Astrophysical Journal|volume=751|issue=2|pages=131|doi=10.1088/0004-637X/751/2/131|issn=0004-637X|arxiv=1111.6585|bibcode=2012ApJ...751..131B}}</ref> Nevertheless, many theories have been proposed to explain the origin of the thick disk component, and among these theories is one that involves minor mergers. In particular, it is speculated that the preexisting thin disk component of a host galaxy is heated during a minor merger and consequently thin disk expands to form a thicker disk component.<ref>{{Cite journal|last=Di Matteo|first=P.|last2=Lehnert|first2=M. D.|last3=Qu|first3=Y.|last4=van Driel|first4=W.|date=January 2011|title=The formation of a thick disk through the heating of a thin disk: Agreement with orbital eccentricities of stars in the solar neighborhood|arxiv=1011.3825|journal=Astronomy & Astrophysics|volume=525|pages=L3|doi=10.1051/0004-6361/201015822|issn=0004-6361|bibcode=2011A&A...525L...3D}}</ref> |
Observations of edge-on galaxies suggest the universal presence of a [[thin disk]], [[thick disk]] and [[Galactic halo|halo]] component of galaxies. Despite the apparent ubiquity of these components, there is still ongoing research to determine if the thick disk and thin disk are truly distinct components.<ref>{{Cite journal|last=Bovy|first=Jo|last2=Rix|first2=Hans-Walter|last3=Hogg|first3=David W.|date=2012|title=The Milky Way Has No Distinct Thick Disk|url=http://stacks.iop.org/0004-637X/751/i=2/a=131|journal=The Astrophysical Journal|volume=751|issue=2|pages=131|doi=10.1088/0004-637X/751/2/131|issn=0004-637X|arxiv=1111.6585|bibcode=2012ApJ...751..131B}}</ref> Nevertheless, many theories have been proposed to explain the origin of the thick disk component, and among these theories is one that involves minor mergers. In particular, it is speculated that the preexisting thin disk component of a host galaxy is heated during a minor merger and consequently thin disk expands to form a thicker disk component.<ref>{{Cite journal|last=Di Matteo|first=P.|last2=Lehnert|first2=M. D.|last3=Qu|first3=Y.|last4=van Driel|first4=W.|date=January 2011|title=The formation of a thick disk through the heating of a thin disk: Agreement with orbital eccentricities of stars in the solar neighborhood|arxiv=1011.3825|journal=Astronomy & Astrophysics|volume=525|pages=L3|doi=10.1051/0004-6361/201015822|issn=0004-6361|bibcode=2011A&A...525L...3D}}</ref> |
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==See also== |
==See also== |
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{{portal|Astronomy}} |
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{{div col|colwidth=30em}} |
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⚫ | |||
*[[Dwarf spheroidal galaxy]] |
*[[Dwarf spheroidal galaxy]] |
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*[[Dwarf elliptical galaxy]] |
*[[Dwarf elliptical galaxy]] |
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* [[Interacting galaxy]] |
* [[Interacting galaxy]] |
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* [[Satellite galaxies of the Milky Way]] |
* [[Satellite galaxies of the Milky Way]] |
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* [[Satellite galaxies of Andromeda]] |
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*[[Ram pressure]] |
*[[Ram pressure]] |
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{{div col end}} |
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==References== |
==References== |