of compact groups of dwarf galaxies. It is only fair to admit that my colleagues by and large do not seem to be impressed, however.

The question is being put to observational tests. Key to the argument for early assembly is the idea that present-day clusters of galaxies yield a consistent scaled picture for young galaxies as irregular mass concentrations at redshift z~10. Ongoing advances in observations of the evolution of the clusters back to z=1 will help test this picture and may offer lessons on how protogalaxies evolved. The exploration of the universe at redshifts greater than unity already has given us a remarkably detailed picture of the history of the galaxies—a complex mix of evolution and stability—the meaning of which is under intense discussion. Further advances in observations of the state of the universe at high redshift will be followed with interest by all sides of the debate on how it all began, what it all might mean, and how it all will end.

This work was supported in part by the National Science Foundation.

1. Peebles, P.J.E. (1988) in The Epoch of Galaxy Formation, eds. Frenk, C.S., Ellis, R.S., Shanks, T., Heavens, A.F. & Peacock, J.A. (Kluwer, Dordrecht, the Netherlands), pp. 1–13.

2. Schramm, D.N. (1998) Proc. Natl. Acad. Sci. USA 95, 42–46.

3. Mushotzky, R. (1998) Proc. Natl. Acad. Sci. USA 95, 72–77.

4. Songaila, A., Wampler, E.J. & Cowie, L.L. (1997) Nature (London) 385, 137–139.

5. Tytler, D., Burls, S. & Kirklin, D. (1997) Astrophys. J., in press.

6. Steidel, C.C. (1998) Proc. Natl. Acad. Sci. USA 95, 22–28.

7. Madau. P., Ferguson, H.C., Dickinson, M.E., Giavalisco, M. Steidel, C.C. & Fruchter. A. (1996) Mon. Not. R. Astron. Soc. 283, 1388–1404.

8. Guzmán, R., Gallego, J., Koo, D.C., Phillips, A.C., Lowenthal, J.D., Faber, S.M., Illingworth, G.D. & Vogt. N.P. (1997) Astrophys. J., in press.

9. Kauffmann, G. (1996) Mon. Not. R. Astron. Soc. 281, 487–492.

10. Prochaska, J.X. & Wolfe, A.M. (1997) Astrophys. J. 487, 73.

11. Efstathiou, G. & Bond, J.R. (1986) Mon. Not. R. Astron. Soc. 218, 103–121.

12. Peebles, P.J.E. (1997) Astrophys. J. 483, L1–L4.

13. Hernquist, L., Katz, N., Weinberg, D.H. & Miralda-Escudé, J. (1996) Astrophys. J. 457, L51–L55.

14. Miralda-Escudé, J., Cen, R., Ostriker, J.P. & Rauch, M. (1996) Astrophys. J. 471, 582–616.

15. Cohen, J.G., Cowie, L.L., Hogg, D.W., Songaila, A., Blanford. R., Hu, E.M. & Shopbell, P. (1996) Astrophys. J. 471, L5–L9.

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement