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Did the Bulge Form All at Once?

Published online by Cambridge University Press:  25 May 2016

R.M. Rich*
Affiliation:
Department of Astronomy, Columbia University, 538 W. 120th St. NY NY 10027

Extract

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It is reasonable to say that if Jan Oort were alive today, he would no doubt find recent developments in the study of the Galactic bulge to be fascinating. Oort considered the Galactic bulge in two contexts. First, he was interested in the use of the RR Lyrae stars as probes to determine the distance to the Galactic Center. No doubt, Oort would have been excited about the growing evidence of the bulge's triaxiality, as well as by the debate over the age of the bulge. His second interest was in the nature of activity at the center, an issue that I will not discuss in this review. The latter also remains an unsolved problem of the Milky Way, and (based on his work) one that might have been nearer to his heart than this one. Yet the question of when the bulge formed is ultimately a question about the formation history of the Galaxy. The oldest stars (those whose ages we are certain of) are found in Galactic globular clusters, the sum total of which are ≈ 5 × 107M⊙. The field population of the bulge is ≈ 2–3 × 1010M⊙, an order of magnitude more massive than the field population of the metal poor spheroid. So if the bulge formed all at once, and early, then the Milky Way had a luminous, even cataclysmic youth. But if the bulge formed later in the history of our galaxy, as a starburst or dynamical instability of the central disk, then the young Milky Way may have been inconspicuous and primeval galaxies may be hard to find indeed. If our bulge formed very early, its stellar population might have much in common with the giant ellipticals, while a late bulge might teach us much about processes that affect galaxy evolution.

Type
Chapter 5: How Did the Milky Way Form?
Copyright
Copyright © Kluwer 1996 

References

Arendt, R.G. et al. 1994, ApJ, 425, 530 Google Scholar
Baade, W. 1951, Pub. Obs. Univ. Mich., 10, 7 Google Scholar
Barbuy, B., Castro, S., Ortolani, S., & Bica, E., 1992 AA, 259, 607 Google Scholar
Baum, W., Light, R.M., Holtzman, J.A. et al. 1993, in Galactic Bulges, Proc. IAU Symp. 153, Dejonghe, H., Habing, H.J., eds, Kluwer, Dordrecht, 289 Google Scholar
Blanco, V.M., 1988, AJ, 95, 1400 Google Scholar
Blitz, L, & Spergel, D.N., 1991, ApJ, 313, 59 Google Scholar
Catchpole, R.M., Whitelock, P.A., & Glass, I.S. 1990, MNRAS, 252, 210 Google Scholar
Combes, F., & Sanders, R.H. 1981, AA, 96, 154 Google Scholar
Dwek, E. et al. 1995 ApJ in press Google Scholar
Glass, I., Whitelock, P.A., Catchpole, R.M., & Feast, M.W. 1995, MNRAS in press.Google Scholar
Greggio, L., & Renzini, A., ApJ, 364, 35 Google Scholar
Matteucci, F., & Brocato, E., ApJ, 365, 539 Google Scholar
McWilliam, A., & Rich, R.M. 1994, ApJS, 91, 749 Google Scholar
McWilliam, A., Tomaney, A., & Rich, R.M. 1995, ApJ, submitted Google Scholar
Mould, J.R. 1993 in Science With the Hubble Space Telescope, Baia Chia Workshop Google Scholar
Minnitti, D.M., White, S.D.M., Olszewski, E.W., & Hill, J.M. 1992, ApJ, 393, L47 CrossRefGoogle Scholar
Minnitti, D., 1994, Ph.D. thesis, University of Arizona Google Scholar
Ortolani, S., Rich, R.M., & Renzini, , 1994 in preparation Google Scholar
Ortolani, S., Renzini, A., et al. 1995, Nature, Submitted Google Scholar
Pfenniger, D., & Norman, C., 1990, Ap.J., 313, 391 Google Scholar
Rees, M.J., & Ostriker, J.P. 1977, MNRAS, 179, 541 Google Scholar
Renzini, A., 1993, in Galactic Bulges, Proc. IAU Symp. 153, Dejonghe, H., Habing, H.J., eds, Kluwer, Dordrecht, 391 Google Scholar
Rich, R.M., 1985, Mem. S. A. It., 56, 23 Google Scholar
Rich, R.M., 1988, AJ, 95, 828 Google Scholar
Rich, R.M., 1990, Ap.J., 362, 604.Google Scholar
Rich, R.M., 1993, in Galactic Bulges, Proc. IAU Symp. 153, Dejonghe, H., Habing, H.J., eds, Kluwer, Dordrecht, 169 Google Scholar
Rich, R.M., Terndrup, D.M., & Sadler, E.M. 1995 in preparation Google Scholar
Sellwood, J.A., & Merritt, D., 1994, ApJ, 425, 530 Google Scholar
Silk, J., 1977, ApJ, 211, 638 Google Scholar
Terndrup, D.M., 1988, AJ, 96, 884 Google Scholar
Terndrup, D.M., Sadler, E., & Rich, R.M. 1995, AJ, in press Google Scholar
van den Bergh, S., 1971, AJ, 76, 1082 Google Scholar
Weiland, J.L. et al. 1994, ApJ, 425, L81 Google Scholar
Wheeler, J.C., Sneden, C., & Truran, J.W. Jr. 1989, ARAA, 27, 279 Google Scholar