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Glossary
The Local Group (of Galaxies)
The Local Group
consists of approximately 30 galaxies laying within about
1 Mpc of the Galaxy.
These galaxies are thought to be loosely gravtitationally bound.
The most prominent members are our Galaxy (the "Milky Way"),
M31 (the Andromeda galaxy),
and M33 (the Triangulum galaxy).
These are all spiral galaxies.
The next most luminous are the so-called
Large and Small
Magellanic Clouds (LMC & SMC).
These are irregular galaxies (with 11
others).
The remaining galaxies are so-called dwarf Ellipticals/spheriods.
(see also 2002 PHYS 316 Notes Lecture-5 and
Lecture-14).
The exact membership of of Local Group (particularly on its
outskirts) remains a matter of some debate.
There appear to be two subgroups within the
Local Group:
- the Galaxy subgroup, consisting of our Galaxy and
a dozen or so other galaxies (including the LMC & SMC)
- the Andromeda subgroup, consisting of M31, M32, M33 and
a handful of other galaxies.
From the observed dynamics of the galaxies, combined with estimates of
the masses, the gravitational center of the Local Group
can be estimated. Most estimates place this approximately
450 kpc away from the Sun in the direction of M31
(Gal coords 120, -21).
The Sun's motion relative to the Local Group can then be estimated.
This calculation involves determining the vector for the Sun's
motion within the Local Standard of Rest (~20 km/s), the orbit of the
Local Standard of Rest around the Galactic Center (~220 km/s), and
our Galaxy's motion with respect to the center of the Local Group.
Most estimates agree that the Sun's motion wrt the Local Group
is 308 km/s in a direction with Galactic Coordinates
+100 deg, -4 deg.
|
Name
|
|
Class
|
v-helio
|
v-LG
(hcat)
|
v-CMB
(hcat)
|
Distance
(kpc)
|
D-LG
(kpc)
|
R |
C |
X |
| Milky Way |
|
Sbc I-II |
... |
+308 |
+371 |
8 |
460 |
... |
... |
... |
| SDG (Sagittarius) |
|
dSph(t) |
+142 |
|
|
30 |
460 |
... |
30 |
53 |
| ESO056-115 (LMC) |
* |
Ir III-IV |
+275 |
+82 |
+355 |
60 |
480 |
... |
... |
... |
| NGC0292 (SMC) |
|
Im IV-V |
+148 |
-7 |
+114 |
58 |
480 |
... |
... |
... |
| DDO199 (Ursa Minor) |
|
dSph |
-247 |
-19 |
-170 |
60 |
430 |
no |
no |
no |
| DDO208 (Draco) |
|
dSph |
-293 |
-66 |
-316 |
80 |
430 |
5 |
no |
? |
| ESO351-030 (Sculptor) |
|
dSph |
+110 |
+141 |
-108 |
90 |
440 |
? |
no |
13 |
| 7ZW828 (Sextans) |
|
dSph |
+226 |
??? |
??? |
90 |
510 |
2 |
no |
no |
| ESO206-020A (Carina) |
|
dSph |
+223 |
-14 |
+339 |
100 |
510 |
9 |
no |
no |
| ESO356-004 (Fornax) |
|
dSph |
53 |
-10 |
-127 |
140 |
450 |
11 |
no |
no |
| DDO 074 (Leo I) |
|
dSph |
+287 |
+97 |
+555 |
250 |
610 |
no |
no |
no |
| DDO 093 (Leo II) |
|
dSph |
+76 |
-83 |
+320 |
210 |
570 |
no |
no |
no |
| ESO245-007 (Phoenix) |
|
dIr/dSph |
+56 |
-16 |
-119 |
400 |
590 |
no |
no |
no |
| NGC6822 |
|
Ir IV-V |
-56 |
+8 |
-254 |
500 |
670 |
lot |
28 |
no |
| NGC0185 |
|
Sph |
-202 |
+54 |
-491 |
660 |
220 |
| NGC0147 |
|
Sph |
-193 |
+133 |
-415 |
660 |
220 |
| IC 10 (UGC 192) |
|
Ir IV |
-344 |
-47 |
-553 |
660 |
270 |
| DDO69 (Leo A) |
|
Ir V |
+24 |
-15 |
+292 |
690 |
880 |
| Cassiopeia (AND VII.) |
|
dSph |
... |
... |
... |
690 |
290 |
| [KK98a]011341.9+330920 (And. II) |
|
dSph |
... |
... |
... |
700 |
260 |
| IC1613 |
|
Ir V |
-232 |
-62 |
-552 |
720 |
470 |
| NGC0224 (M31) |
|
Sb I-II |
-301 |
-14 |
-576 |
760 |
300 |
| NGC0221 (M32) |
|
E2 |
-205 |
+73 |
-490 |
760 |
310 |
| NGC0205 (M110) |
|
Sph |
-244 |
+52 |
-511 |
760 |
310 |
| PGC002121 (AND III.) |
|
dSph |
... |
... |
... |
760 |
310 |
| DDO 216 (Pegasus) |
|
Ir V |
-182 |
+61 |
-539 |
760 |
440 |
| NGC0598 (M33) |
|
Sc II-III |
-181 |
+68 |
-454 |
790 |
370 |
| PGC002666 (AND I.) |
|
dSph |
... |
... |
... |
810 |
360 |
| (AND V.) |
|
dSph |
... |
... |
... |
810 |
370 |
| LGS3 (Pisces) |
|
dIr/dSph |
-286 |
-14 |
-576 |
810 |
420 |
| Peg dSph (And VI.) |
|
dSph |
... |
... |
... |
830 |
430 |
| DDO210 (Aquarius) |
? |
IBm V |
-131 |
-32 |
-405 |
1020 |
1020 |
| EQ 2238-646 (Tucana) |
? |
dSph |
... |
... |
... |
870 |
1100 |
| DD0221 (WLM) |
|
IBr IV-V |
-120 |
-7 |
-447 |
930 |
790 |
| ESO594-4 (Sag DIG) |
? |
Ir V |
-79 |
-36 |
-253 |
1400 |
1480 |
|