Local Group

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The Local Group of galaxies. The Milky Way and Andromeda are the most massive galaxies by far. (Click to enlarge)
Distribution of the iron content (in logarithmic scale) in four dwarf neighbouring galaxies of the Milky Way.

The Local Group is the galaxy group that includes the Milky Way. The Local Group comprises more than 54 galaxies, most of them dwarf galaxies. Its gravitational center is located somewhere between the Milky Way and the Andromeda Galaxy. The Local Group covers a diameter of 10 Mly (3.1 Mpc) and has a binary (dumbbell)[1] distribution. The group itself is a part of the larger Laniakea Supercluster (i.e., the Local Supercluster).[2] The local supercluster was previously thought to be the Virgo Supercluster, now an appendage to the newly defined local supercluster.[3]

The two most massive members of the group are the Milky Way and Andromeda galaxies.[citation needed] These two spiral galaxies each has a system of satellite galaxies.

History[edit]

The term "The Local Group" was introduced by Edwin Hubble in Chapter VI of his book The Realm of the Nebulae (Hubble 1936, pp. 124–151). There, he described it as "a typical small group of nebulae which is isolated in the general field". He delineated, by decreasing luminosity, its members to be M31, Milky Way, M33, Large Magellanic Cloud, Small Magellanic Cloud, M32, NGC 205, NGC 6822, NGC 185, IC 1613 and NGC 147. He also identified IC 10 as a possible Local Group member. By 2003, the number of known Local Group members has increased from his initial 12 to 36 by way of the discovery of almost two dozen[clarify] low-luminosity galaxies.[5]

Component galaxies[edit]

Map[edit]

Sextans B Sextans A Milky Way Leo I (dwarf galaxy) Canes Dwarf Leo II (dwarf galaxy) NGC 6822 Phoenix Dwarf Tucana Dwarf Wolf-Lundmark-Melotte Cetus Dwarf IC 1613 SagDIG Aquarius Dwarf Triangulum Galaxy NGC 185 NGC 147 IC 10 Andromeda Galaxy M110 Leo A NGC 3109 Antlia Dwarf LGS 3 Pegasus Dwarf Andromeda II Andromeda III Andromeda I
About this image
Local Group (clickable map)

Galactic bodies[edit]

Spiral galaxies
name type constellation notes
Milky Way SBbc Sagittarius (centre) Where we reside.
Andromeda Galaxy (M31, NGC 224) SA(s)b Andromeda With ~220 kly in diameter, it is the largest and most massive galaxy in the group
Triangulum Galaxy (M33, NGC 598) SA(s)cd Triangulum Third largest, only unbarred spiral galaxy and possible satellite of the Andromeda Galaxy.
Elliptical galaxies
name type constellation notes
M32 (NGC 221) E2 Andromeda satellite of the Andromeda Galaxy
Irregular galaxies
name type constellation notes
Wolf–Lundmark–Melotte (WLM, DDO 221) Ir+ Cetus
IC 10 KBm or Ir+ Cassiopeia
Small Magellanic Cloud (SMC, NGC 292) SB(s)m pec Tucana satellite of Milky Way
Canis Major Dwarf Irr Canis Major satellite of Milky Way
Pisces Dwarf (LGS3) Irr Pisces satellite of the Triangulum Galaxy?
IC 1613 (UGC 668) IAB(s)m V Cetus
Phoenix Dwarf Irr Phoenix
Large Magellanic Cloud (LMC) Irr/SB(s)m Dorado Fourth largest member of the group, satellite of Milky Way
Leo A (Leo III) IBm V Leo
Sextans B (UGC 5373) Ir+IV-V Sextans
NGC 3109 Ir+IV-V Hydra
Sextans A (UGCA 205) Ir+V Sextans
Dwarf elliptical galaxies
name type constellation notes
M110 (NGC 205) dE6p Andromeda satellite of the Andromeda Galaxy
NGC 147 (DDO 3) dE5 pec Cassiopeia satellite of the Andromeda Galaxy
SagDIG (Sagittarius Dwarf Irregular Galaxy) IB(s)m V Sagittarius Most remote from barycenter member thought to be in the Local Group.[6]
NGC 6822 (Barnard's Galaxy) IB(s)m IV-V Sagittarius
Pegasus Dwarf (Pegasus Dwarf Irregular, DDO 216) Irr Pegasus
Dwarf spheroidal galaxies
name type constellation notes
Boötes I dSph Boötes
Cetus Dwarf dSph/E4 Cetus
Canes Venatici I Dwarf and Canes Venatici II Dwarf dSph Canes Venatici
KKs 3 dSph
Andromeda III dE2 Andromeda satellite of the Andromeda Galaxy
NGC 185 dE3 pec Cassiopeia satellite of the Andromeda Galaxy
Andromeda I dE3 pec Andromeda satellite of the Andromeda Galaxy
Sculptor Dwarf (E351-G30) dE3 Sculptor satellite of Milky Way
Andromeda V dSph Andromeda satellite of the Andromeda Galaxy
Andromeda II dE0 Andromeda satellite of the Andromeda Galaxy
Fornax Dwarf (E356-G04) dSph/E2 Fornax satellite of Milky Way
Carina Dwarf (E206-G220) dE3 Carina satellite of Milky Way
Antlia Dwarf dE3/dSph/Irr? Antlia
Leo I (DDO 74) dE3 Leo satellite of Milky Way
Sextans Dwarf dE3 Sextans satellite of Milky Way
Leo II (Leo B) dE0 pec Leo satellite of Milky Way
Ursa Minor Dwarf dE4 Ursa Minor satellite of Milky Way
Draco Dwarf (DDO 208) dE0 pec Draco satellite of Milky Way
SagDEG (Sagittarius Dwarf Elliptical Galaxy) dSph/E7 Sagittarius satellite of Milky Way
Tucana Dwarf dE5 Tucana
Cassiopeia Dwarf (Andromeda VII) dSph Cassiopeia satellite of the Andromeda Galaxy
Pegasus Dwarf Spheroidal Galaxy (Andromeda VI) dSph Pegasus satellite of the Andromeda Galaxy
Ursa Major I Dwarf and Ursa Major II Dwarf dSph Ursa Major satellite of Milky Way
Leo IV dSph Leo satellite of the Milky Way
Leo V dSph Leo satellite of the Milky Way
Leo T dSph/Irr Leo satellite of the Milky Way
Boötes II dSph Boötes satellite of the Milky Way
Boötes III dSph Boötes satellite of the Milky Way
Coma Berenices dSph Coma Berenices satellite of the Milky Way
Segue 2 dSph Aries satellite of the Milky Way
Hercules dSph Hercules satellite of the Milky Way
Pisces II dSph Pisces satellite of the Milky Way
Reticulum II dSph Reticulum satellite of the Milky Way
Eridanus II dSph Eridanus satellite of the Milky Way
Grus dSph Grus satellite of the Milky Way
Tucana II dSph Tucana satellite of the Milky Way
Identification Unclear
name type constellation notes
Virgo Stellar Stream dSph (remnant)? Virgo In the process of merging with the Milky Way
Willman 1 dwarf Spherical galaxy
or Globular cluster?
Ursa Major 147,000 light-years away
Andromeda IV Irr? Andromeda probably not a galaxy
UGCA 86 (0355+66) Irr, dE or S0 Camelopardalis
UGCA 92 (EGB0427+63) Irr or S0 Camelopardalis
Horologium dSph or Globular Cluster Horologium satellite of the Milky Way
Pictoris dSph or Globular Cluster Pictor satellite of the Milky Way
Phoenix II dSph or Globular Cluster Phoenix satellite of the Milky Way
Indus dSph or Globular Cluster Indus satellite of the Milky Way
Eridanus III dSph or Globular Cluster Eridanus satellite of the Milky Way
Probable non-members
name type constellation notes
GR 8 (DDO 155) Im V Virgo
IC 5152 IAB(s)m IV Indus
NGC 55 SB(s)m Sculptor
Aquarius Dwarf (DDO 210) Im V Aquarius
NGC 404 E0 or SA(s)0 Andromeda
NGC 1569 Irp+ III-IV Camelopardalis
NGC 1560 (IC 2062) Sd Camelopardalis
Camelopardalis A Irr Camelopardalis
Argo Dwarf Irr Carina
ESO 347-8 (2318–42) Irr Grus
UKS 2323-326 Irr Sculptor
UGC 9128 (DDO 187) Irp+ Boötes
Sextans C
objects in local group no longer recognised as galaxies
name type constellation notes
Palomar 12 (Capricornus Dwarf) Capricornus a globular cluster formerly classified as a dwarf spheroidal galaxy
Palomar 4 (originally designated Ursa Major Dwarf) Ursa Major a globular cluster formerly classified as a dwarf spheroidal galaxy

Other notable objects[edit]

Diagram[edit]

A diagram of our location in the observable universe. (Click here for smaller image.)

See also[edit]

References[edit]

  1. ^ Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics 49 (1): 3–18. Bibcode:2006Ap.....49....3K. doi:10.1007/s10511-006-0002-6. 
  2. ^ Gillman, Ollie. "The road map to the Universe". Daily Mail. Daily Mail. Retrieved 24 April 2015. 
  3. ^ Gibney, Elizabeth. "Earth's new address: 'Solar System, Milky Way, Laniakea'". Nature. Nature. Retrieved 24 April 2015. 
  4. ^ Miller, Bryan W. et al. (December 2001), "The Star Formation History of LGS 3", The Astrophysical Journal 562 (2): 713–726, arXiv:astro-ph/0108408, Bibcode:2001ApJ...562..713M, doi:10.1086/323853 
  5. ^ van den Bergh, Sidney (May 2003). "History of the Local Group". To be published in: "The Local Group as an Astrophysical Laboratory" (Cambridge University Press): 5042. arXiv:astro-ph/0305042. Bibcode:2003astro.ph..5042V. 
  6. ^ van den Bergh, Sidney (April 2000). "Updated Information on the Local Group". The Publications of the Astronomical Society of the Pacific 112 (770): 529–536. arXiv:astro-ph/0001040. Bibcode:2000PASP..112..529V. doi:10.1086/316548. 
  7. ^ Wakker, B. P.; York, D. G.; Wilhelm, R.; Barentine, J. C.; Richter, P.; Beers, T. C.; Ivezić, Ž.; Howk, J. C. (2008). "Distances to Galactic High‐Velocity Clouds. I. Cohen Stream, Complex GCP, Cloud g1". The Astrophysical Journal 672 (1): 298–319. arXiv:0709.1926. Bibcode:2008ApJ...672..298W. doi:10.1086/523845. 
  8. ^ "Massive Gas Cloud Speeding Toward Collision With Milky Way". Retrieved 2008-06-06. 

External links[edit]

Media related to Local Group at Wikimedia Commons