Christine Kronberg <smil@lrz.uni-muenchen.de>

This is "our" group of galaxies.  It was first recognized by Hubble,
in the time of the first distance determinations and redshift
measurements.

The Local Group contains the Andromeda Galaxy (M31) and its satellites
M32 and M110, as well as the Triangulum galaxy (M33).  Other members
(over 30 in all) include our Milky Way Galaxy, the Large and the Small
Magellanic Cloud (LMC and SMC), which have been known before the
invention of the telescope (as was the Andromeda Galaxy), as well as
several smaller galaxies which were discovered more recently.  These
galaxies are spread in a volume of nearly 10 million light years
diameter, centered somewhere between the Milky Way and M31.
Membership is not certain for all these galaxies, and there are
possible other candidate members.

Of the Local Group member galaxies, the Milky Way and M31 are by for
the most massive, and therefore dominant members. Each of these two
giant spirals has accumulated a system of satellite galaxies, where

* the system of the Milky Way contains many (nearby) dwarf galaxies,
spread all over the sky, namely Sag DEG, LMC, SMC, and the dwarf
galaxies in Ursa Minor, Draco, Carina, Sextans (dwarf), Sculptor,
Fornax, Leo I and Leo II; and

* the system of the Andromeda galaxy is seen from outside, and thus
grouped around its main galaxy M31 in Andromeda, containing bright
nearby M32 and M110 as well as fainter and more far-out NGC 147 and
185, the very faint systems And I, And II, And III, and, possibly, And
IV.

The third-largest galaxy, the Triangulum spiral 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 cannot be assigned to one of the main subgroups, and
float quite alone in the gravitational field of 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 have probably been once part of our
galaxy group.

As this shows, the Local Group is not isolated, but in gravitational 
interaction, and member exchange, with the nearest surrounding groups, 
notably:

* the Maffei 1 group, which besides the giant elliptical galaxy Maffei
1 also contains smaller Maffei 2, and is associated with nearby IC
342.  This group is highly obscured by dark dust near the Milky Way's
equatorial plane.

* the Sculptor Group or South Polar Group (with members situated
around the South Galactic pole), dominated by NGC 253; 

* 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 perhaps collide and merge in some distant
future, to form a giant elliptical.  In addition, 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 so that it will finally fall and merge into
this huge cluster of galaxies.

A table of the currently known Local Group member galaxies is at
<URL:http://www.seds.org/messier/more/local.html>.  A (somewhat
technical) review of the Local Group is at
<URL:http://arXiv.org/abs/astro-ph/?0001040>.