The Local Group.
The Local Group is a collection of more than 40 galaxies, spread across a volume of space some 10 million light-years in diameter, of which our own Milky Way Galaxy and the Andromeda Galaxy are the dominant and central members. Both these two giant spirals have retinues of satellite galaxies, which together account for most of the membership of the Local Group.
The Milky Way's satellites include: the Large Magellanic Cloud, the Small Magellanic Cloud, the Sagittarius Dwarf Elliptical, the Ursa Minor Dwarf, the Draco Dwarf, the Carina Dwarf, the Sextans Dwarf, the Sculptor Dwarf, the Fornax Dwarf, Leo I, and Leo II. Among the retinue of the Andromeda Galaxy are: M32 , M110, the fainter and more faraway NGCs 147 and 185, the very faint systems And I, And II, And III, and possibly And IV, And V, And VI (the Pegasus Dwarf), and And VII (the Cassiopeia Dwarf). The third-largest galaxy, the Triangulum Galaxy (M33), may or may not be an outlying gravitationally-bound companion of M31, but has itself probably the dwarf LGS 3 as a satellite. The other members of the Local Group, including the Antlia Dwarf and Wolf-Lundmark-Melotte Galaxy, fall outside the main subgroups and float alone in the gravitational seas between the giant group members.
The substructures of the group are probably not stable. Observations and calculations suggest that the group is highly dynamic and has changed significantly in the past. The galaxies around the large elliptical Maffei 1 (see Maffei 1 Group, for example, were probably once part of our galaxy group. Indeed, the Local Group is not isolated but is in gravitational interaction and member exchange with the nearest surrounding groups, notably the Maffei 1 Group, the Sculptor Group, the M81 Group, and the M83 Group. In the future, interaction between the member galaxies and with the cosmic neighborhood will continue to change the Local Group. Some astronomers speculate that the two large spirals, our Milky Way and the Andromeda Galaxy, may collide and merge to form a giant elliptical. Also, there is evidence that our nearest big cluster of galaxies, the Virgo Cluster, will probably stop our cosmological recession away from it, accelerate the Local Group toward itself, and so eventually assimilate the Local Group into its collection.
|galaxy||RA||Dec||type||abs mag||diameter (ly)||rad vel (km/s)||distance (ly)|
|Milky Way Galaxy||17:45.6||-28:56||SBbc I-II||-20.6||90,000||0||28,000|
|Sagittarius Dwarf Elliptical||18:55||-30:30||dSph(E7)||-14.0||10,000||78,000|
|Large Magellanic Cloud||05:19.7||-68:57||Irr III-IV||-18.1||30,000||+119||179,000|
|Small Magellanic Cloud||00:51.7||-73:14||Irr IV-V||-16.2||16,000||+34||210,000|
|Ursa Minor Dwarf||15:08.8||+67:12||dSph||-8.9||2,000||-47||215,000|
|NGC 6822 (Barnard's Galaxy)||19:44.9||-14:49||Irr IV-V||-16.4||8,000||+44||1,600,000|
|Leo III (Leo A)||09:59.4||+30:45||dIrr||-11.7||4,000||-19||2,250,000|
|IC 1613||01:05.1||+02:08||Irr V||-14.9||10,000||-152||2,300,000|
|Aquarius Dwarf||20:46.8||-12:51||dIrr/dSph 2||-23||2,600,000|
|LGS 3 (Pisces Dwarf)||01:03.8||+21:53||dIrr/dSph||-9.7||2,000||-149||2,650,000|
|Andromeda Galaxy (M31)||00:42.7||+41:16||Sb I-II||-21.1||140,000||-121||2,650,000|
|M110 (NGC 205)||00:41.3||+41:41||dSph/dE5||-16.3||15,000||-60||2,650,000|
|Triangulum Galaxy (M33)||01:33.9||+30:39||Sc II-III||-18.9||55,000||-46||2,850,000|
|Sagittarius Dwarf Irregular||19:30.1||-17:42||dIrr||-11.0||3,000||+8||3,450,000|
|NGC 3109||10:03.1||-26:09||Irr IV-V||-15.8||25,000||+194||4,100,000|