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

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

For a Pdf version of the article, click here.
For a Postscript version of the article, click here.


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.


Table of Contents

MOTIVATION AND SCOPE OF REVIEW
Introduction
Preconception Number 1: Bulges Are Old
Preconception Number 2: The Galactic Bulge Is Super-Solar Metallicity
Preconception Number 3: Bulges Are Similar to Elliptical Galaxies

RESOLVED BULGES - LOCAL GROUP GALAXIES
Milky Way Galaxy
M 33 (NGC 598)
M 31 (NGC 224)
Large Magellanic Cloud
General Properties of the Local Group Disk Galaxies

LOW-REDSHIFT UNRESOLVED BULGES
Bulges and Ellipticals
Bulges and Disks
Bulges in Formation at z < 0.1?

HIGH-REDSHIFT BULGES

FORMATION SCENARIOS
Are Bulges Related to Their Haloes?
Accretion/Merging
Disk-Bars-Bulges, Etc

CONCLUSIONS

REFERENCES

Next