Local Group

The Local Group is the group of galaxies that includes our galaxy, the Milky Way. The group comprises over 35 galaxies, with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy. The galaxies of the Local Group cover a 10 million light-year diameter (see 1 E+22 m for distance comparisons) and have a binary (dumbbell)cite journal
author=Karachentsev, I. D.; Kashibadze, O. G.
title=Masses of the local group and of the M81 group estimated from distortions in the local velocity field
journal=Astrophysics
year=2006
volume=49
issue=1
pages=3–18
url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006Ap.....49....3K | doi = 10.1007/s10511-006-0002-6 ] shape. The group is estimated to have a total mass of (1.29 ± 0.14)e|12M_☉.The group itself is one of many within the Virgo Supercluster (i.e. the Local Supercluster).cite journal
author= R. B. Tully
title=The Local Supercluster
journal=Astrophysical Journal
year=1982
volume=257
pages=389–422
url=http://adsabs.harvard.edu/abs/1982ApJ...257..389T | doi = 10.1086/159999 ]

The two most massive members of the group are the Milky Way and the Andromeda Galaxy. These two barred spirals each have a system of satellite galaxies.
* The Milky Way's satellite system consists of Sagittarius Dwarf Galaxy, Large Magellanic Cloud, Small Magellanic Cloud, Canis Major Dwarf, Ursa Minor Dwarf, Draco Dwarf, Carina Dwarf, Sextans Dwarf, Sculptor Dwarf, Fornax Dwarf, Leo I, Leo II, and Ursa Major Dwarf.
* Andromeda's satellite system comprises M32, M110, NGC 147, NGC 185, And I, And II, And III, And IV, And V, Pegasus dSph, Cassiopeia Dwarf, And VIII, And IX, and And X.
* The Triangulum Galaxy, the third largest and only ordinary spiral galaxy in the Local Group, may or may not be a companion to the Andromeda galaxy but probably has Pisces Dwarf as a satellite. The other members of the group are gravitationally secluded from these large subgroups: IC1613, Phoenix Dwarf, Leo A, Tucana Dwarf, Cetus Dwarf, Pegasus Dwarf Irregular, Wolf-Lundmark-Melotte, Aquarius Dwarf, and Sagittarius Dwarf Irregular.

History

Edwin Hubble was the first to identify the Local Group in Chapter VI of his book "The Realm of Nebulae" (Hubble 1936, pp. 124–151). There he describes it as "a typical small group of nebulae which is isolated in the general field." In that book, he delineated by decreasing luminosity its members to be M31, the Milky Way, M33, the Large Magellanic Cloud, the 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. In the ~70 years since his work, the number of known Local Group members has increased from his initial twelve to thirty-six as of 2003, by way of the discovery of almost two dozen low-luminosity galaxies.citation
last1 = van den Bergh
first1 = Sidney
authorlink1 = Sidney van den Bergh
title = History of the Local Group
year = 2003
date = May 2003
journal = To be published in: "The Local Group as an Astrophysical Laboratory"
publisher = Cambridge University Press
url = http://adsabs.harvard.edu/abs/2003astro.ph..5042V]

Component galaxies

Clickable maps

circle 167 27 20 Sextans Bcircle 120 36 23 Sextans Acircle 318 239 20 Milky Waycircle 289 197 16 Leo I (dwarf galaxy)circle 334 201 15 Canes Dwarfrect 303 185 318 215 Leo II (dwarf galaxy)circle 357 289 28 NGC 6822circle 288 323 24 Phoenix Dwarfcircle 248 391 35 Tucana Dwarfcircle 363 416 20 Wolf-Lundmark-Melottecircle 363 383 17 Cetus Dwarfcircle 369 346 11 IC 1613rect 381 335 393 357 SagDIGrect 393 335 406 356 Aquarius Dwarfcircle 417 304 17 Triangulum Galaxycircle 417 254 15 NGC 185rect 432 237 447 260 NGC 147circle 461 229 17 IC 10poly 440 282 455 260 511 259 493 285 Andromeda Galaxypoly 450 264 434 265 431 280 442 280 Messier 110circle 295 110 20 Leo Acircle 84 128 20 NGC 3109circle 109 149 14 Antlia Dwarfcircle 412 332 12 LGS 3circle 460 361 21 Pegasus Dwarfcircle 394 272 14 Andromeda IIrect 427 279 438 294 Andromeda IIIrect 438 282 450 294 Andromeda I

desc bottom-left

Milky Way's satellite galaxies (clickable map)

rect 289 219 352 251 Milky Wayrect 319 252 380 281 Sagittarius Dwarf Elliptical Galaxyrect 187 81 229 113 Sextans Dwarfrect 168 273 249 318 Large Magellanic Cloudrect 229 326 288 368 Small Magellanic Cloudrect 297 376 352 407 Sculptor Dwarfrect 183 446 234 476 Fornax Dwarfrect 107 297 150 332 Carina Dwarfrect 296 107 339 144 Bootes Dwarfrect 336 180 408 196 Ursa Major IIrect 357 40 423 59 Ursa Major Irect 370 110 428 142 Ursa Minor Dwarfrect 430 119 470 154 Drwaco Dwarf

desc bottom-left

Galactic bodies

Other notable objects

* Smith's Cloud - High velocity cloud, between 32,000 and 49,000 light years from Earth,cite journal | doi=10.1086/523845 | title=Distances to Galactic High‐Velocity Clouds. I. Cohen Stream, Complex GCP, Cloud g1 | year=2008 | author=Wakker, B. P. | journal=The Astrophysical Journal | volume=672 | pages=298 ] and 8000 light years the disk of the Milky Way Galaxy. [cite web |url=http://www.nrao.edu/pr/2008/smithscloud/ |title=Massive Gas Cloud Speeding Toward Collision With Milky Way|accessdate=2008-06-06 ]
* HVC 127-41-330 - High velocity cloud, 2.3 million light-years from Earth

ee also

* Groups and clusters of galaxies
* List of nearest galaxies
* List of galaxy clusters
* Local Supercluster
* Andromeda's satellite galaxies
* Milky Way's satellite galaxies

References

External links

* [http://www.seds.org/messier/more/local.html The Local Group of Galaxies] , SEDS Messier pages
* [http://www.lowell.edu/users/massey/lgsurvey/ A Survey of the Resolved Stellar Content of Nearby Galaxies Currently Forming Stars] , Lowell Observatory
*