The Local Group

1
The Local Group

• Chang, Seo-Won

2
Definition

• The loose collection of galaxies to which the
  Milky Way belongs is known as the Local Group.
• The criteria of membership
• Within a distance of 1.5Mpc
• Whether or not gravitational bound
• - Radial velocities of nearby galaxies
• - total mass of the Local Group?
• ? Membership is NOT an entirely static property.

3
Definition

• Integral frequency of galaxy distances from the
  Local Group barycenter (Courteau van den
  Bergh1999)
• Mv lt -10.0
• 71 of all Local Group galaxies within 0.5 Mpc
  of the barycenter

4
Definition
5
Local Group Members

• Despite the absence of a clear-cut criterion,
  there is general agreement that the 35 galaxies
  belong to the Local Group (See Table 4.3)
• Spirals Milky Way(Sbc), M31(Sb), M33(Sc)
• Several Dwarf ellipicals, dwarf spheroidals, and
  Irregulars
• What is your first impression of our Local Group?
  

6
Sidney van den Bergh (2000)
7
Local Main-Group

• Milky Way System
• - Sag DEG, LMC, SMC, Canis Major Dwarf
• - Ursa Minor, Draco, Carina, Sextans dwarf
  galaxies
• - Sculptor, Fornax, Leo I, Leo II, Phoenix Dwarf,
  and
• Leo A

8
LMC
SMC
9
Local Main-Group

• Andromeda System
• - M32, M110, NGC 147, NGC 185
• - And I, And II, And III and And IVX
• - M33, LGS 3, IC 1613, UGCA 86 and 92

10
Local Sub-Group

• NGC 3109 system
• - Sextans A and B, Antlia Dwarf and Leo A

11
Local Group Members

• The system lacks any real symmetry
• Two main groups (MW, M31) and one sub-group
• (NGC 3109)
• ? Similar line-of-sight velocities, it would
  appear that
• they represent physical associations. BUT
• some members seem to follow more solitary
  orbits.
• ? All we can say with reasonable confidence is
  that more than 90 of the galaxies in the Local
  Group have absolute mag. fainter than Mv -18.

12
Problems
13
Dynamics
14
Other type Members
15
Other type Members
16
Other type Members
17
Application

• Studying galaxy formation and evolution
• The Star Formation History (SFH), and its
  influence on galaxy evolution, through
  (1) CMD, (2) spectroscopic abundance, (3)
  analysis of variables, and (4) study of the MW
  cluster system
• The mass assembly and the dynamical evolution of
  each system, through
  (1) stellar population
  gradients and kinematics of stars of different
  ages, (2) the dynamics of the LC and interactions
  on galaxy evolution

18
(No Transcript)