The present note updates the information published in my recent monograph on The Galaxies of the Local Group. Highlights include (1) the addition of the newly discovered Cetus dwarf spheroidal as a certain member of the Local Group; (2) an improved distance for the Sagittarius dwarf irregular galaxy (SagDIG), which now places this object very close to the edge of the Local Group zero-velocity surface; (3) more information on the evolutionary histories of some individual Local Group members; and (4) improved distance determinations to, and luminosities for, a number of Local Group members. These data increase the number of certain (or probable) Local Group members to 36. The spatial distribution of these galaxies supports Hubble's claim that the Local Group ``is isolated in the general field.'' Currently available evidence suggests that star formation continued much longer in many dwarf spheroidals than it did in the main body of the Galactic halo. It is suggested that ``young'' globular clusters, such as Ruprecht 106, might have formed in now defunct dwarf spheroidals. Assuming SagDIG, which is the most remote Local Group galaxy, to lie on, or just inside, the zero-velocity surface of the Local Group yields a dynamical age >~17.9+/-2.7 Gyr. However, this value is meaningful only if the outer regions of the local Group are in virial equilibrium.
Publications of the Astronomical Society of the Pacific
- Pub Date:
- April 2000
- GALAXIES: CLUSTERS: GENERAL;
- GALAXIES: LOCAL GROUP;
- 19 pages, 1 figure, to be published in the April 2000 issue of PASP