Published in "Galactic bulges": proceedings of the 153rd Symposium of the International Astronomical Union held in Ghent, Belgium, August 17-22, 1992. Edited by Herwig DeJonghe and Harm Jan Habing. International Astronomical Union. Symposium no. 153, Kluwer Academic Publishers, Dordrecht, p.209

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Abstract. Recent work on the dynamics of galaxy bulges has been dominated by two themes. (1) Bulges share the richness in kinematic structure that is currently being discovered in elliptical galaxies. This includes kinematic evidence for triaxiality and for accretion (counterrotating gas and stellar components). (2) The main subject of this paper is observational and theoretical evidence that some "bulges" are built secularly out of disk material. Many bulges show photometric and kinematic evidence for disklike dynamics. This includes (i) velocity dispersions much smaller than those predicted by the Faber-Jackson - M_B correlation, (ii) rapid rotation V(r) that implies V / values well above the "oblate line" describing rotationally flattened, isotropic spheroids in the V / - ellipticity diagram, and (iii) spiral structure dominating the r^1/4 part of the galaxy. In these galaxies, the steep, r^1/4-law central brightness profiles belong not to bulges but to disks. That is, some galaxy disks have central brightness profiles that are much steeper than the inward extrapolation of an exponential fit to the outer parts. These observations and n-body simulations of gas flow in nonaxisymmetric galaxies imply that high-central-concentration, flat components can be formed out of disk gas that is transported toward the center by bars and oval distortions. The n-body models suggest further that some "bulges" are built of disk stars heated in the axial direction by resonant scattering off of bars. These effects are signs that important secular evolution processes are at work in galaxy disks.

Key words: Galaxy Bulges - Galaxy Disks - Stellar Dynamics - Secular Evolution

Table of Contents

• INTRODUCTION
• STELLAR DYNAMICS OF BULGES: COMPARISON WITH ELLIPTICAL GALAXIES
• The Dynamical Importance of Rotation
• Kinematic (Sub)Structure in Bulges and Elliptical Galaxies
• CYLINDRICAL ROTATION IN BOX-SHAPED BULGES
• SOME BULGES ARE REALLY DISKS
• NGC 4736
• NGC 4826
• NGC 7457
• Many "Bulges" Look as Flat as Disks
• Nuclear Disks
• Triaxial Disklike "Bulges" in Barred Galaxies
• "Bulges" Made of Population I Material
• Conclusions
• BUILDING "BULGES" BY SECULAR EVOLUTION. I. MAKING BULGELIKE DISKS BY BAR-DRIVEN INWARD GAS TRANSPORT
• BUILDING "BULGES" BY SECULAR EVOLUTION. II. MAKING BOX-SHAPED BULGES BY BAR-DRIVEN VERTICAL DISK HEATING
• CONCLUSION: OUR GALAXY
• REFERENCES

^* Visiting Astronomer at the Canada-France-Hawaii Telescope (CFHT), operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique of France, and the University of Hawaii.