Annu. Rev. Astron. Astrophys. 1997. 35: 637-675
Copyright © 1997 by Annual Reviews. All rights reserved

Reprinted with kind permission from Annual Reviews, 4139 El Camino Way, Palo Alto, California, USA

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GALACTIC BULGES

Rosemary F. G. Wyse

Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA;
e-mail: wyse@pha.jhu.edu

Gerard Gilmore

Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, United Kingdom;
Institut d'Astrophysique de Paris, 98bis boulevard Arago, Paris, 75014 France;
e-mail: gil@ast.cam.ac.uk

Marijn Franx

Kapteyn Astronomical Institute, University of Groningen, PO Box 800, Groningen, 9700AV The Netherlands;
e-mail: franx@astro.rug.nl

Key words. galaxy formation, the Galaxy, extragalactic astronomy, Local Group, dynamical astronomy

ABSTRACT. We discuss the present observational and theoretical understanding of the stellar populations of bulges and their implications for galaxy formation and evolution. The place of bulges as key to the Hubble Sequence remains secure, but some old paradigms are giving way to new ones as observations develop. Detailed studies of Local Group bulges and haloes provide a basis on which we consider higher redshift data. We present the evidence for and against the currently common preconceptions that bulges are old, above solar metallicity in the mean, and simply scaled-down versions of ellipticals. We conclude life is not so simple: Bulges are diverse and heterogeneous, and although their properties vary systematically, sometimes they are reminiscent of disks, sometimes of ellipticals. The extant observational data are, however, limited. New and future surveys will rectify this, and we discuss the questions those data will address.

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