Published in "Galactic Bulges", Astrophysics and Space Science Library, Volume 418. ISBN 978-3-319-19377-9. Springer International Publishing Switzerland, 2016, p. 431.
http://arxiv.org/abs/1504.03330

For a PDF version of the article, click here.

ELLIPTICAL GALAXIES AND BULGES OF DISK GALAXIES: SUMMARY OF PROGRESS AND OUTSTANDING ISSUES

John Kormendy

Department of Astronomy, University of Texas at Austin, 2515 Speedway, Mail Stop C1400, Austin, Texas 78712-1205, USA


Abstract: Bulge components of disk galaxies are the high-density centers interior to their outer disks. Once thought to be equivalent to elliptical galaxies, their observed properties and formation histories turn out to be richer and more varied than those of ellipticals. This book reviews progress in many areas of bulge studies. Two advances deserve emphasis: (1) Observations divide bulges into “classical bulges” that look indistinguishable from ellipticals and “pseudobulges” that are diskier and (except in S0s) more actively star-forming than are ellipticals. Classical bulges and ellipticals are thought to form by major galaxy mergers. Disky pseudobulges are a product of the slow (“secular”) evolution of galaxy disks. Nonaxisymmetries such as bars and oval distortions transport some disk gas toward the center, where it starbursts and builds a dense central component that is diskier in structure than are classical bulges. Secular evolution explains many regular structures (e.g., rings) seen in galaxy disks. It is a new area of galaxy evolution work that complements hierarchical clustering. (2) Studies of high-redshift galaxies reveal that their disks are so gas-rich that they are violently unstable to the formation of mass clumps that sink to the center and merge. This is an alternative channel for the formation of classical bulges.

This chapter summarizes big-picture successes and unsolved problems in the formation of bulges and ellipticals and their coevolution (or not) with supermassive black holes. I present an observer'ss perspective on simulations of cold dark matter galaxy formation including baryonic physics. Our picture of the quenching of star formation is becoming general and secure at redshifts z < 1. I conclude with a list of major uncertainties and problems. The biggest challenge is to produce realistic bulges+ellipticals and realistic disks that overlap over a factor of >1000 in mass but that differ from each other as we observe over that whole range. A related difficulty is how hierarchical clustering makes so many giant, bulgeless galaxies in field but not cluster environments. I present arguments that we rely too much on star-formation feedback and AGN feedback to solve these challenges.


Table of Contents

INTRODUCTION

SECULAR EVOLUTION AND THE FORMATION OF PSEUDOBULGES
Enlarged List of Bulge-Pseudobulge Classification Criteria
Secular Evolution in Disk Galaxies: Applications

GIANT CLUMPS IN HIGH-Z GAS-RICH DISKS MAKE CLASSICAL BULGES

MAKING CLASSICAL BULGES AND ELLIPTICALS BY MAJOR MERGERS
Observer's Perspective on Bulge Formation Via Major Mergers
Observed Properties of Ellipticals: Clues to Their Formation
Classical Bulges Resemble Coreless-Disky-Rotating Ellipticals
The Critically Important Target for Galaxy Formation
Critical Obserational Clue: The Problem of Giant, Pure-Disk Galaxies Depends on Environment, Not on Galaxy Mass
It is not a problem that major mergers are rare
Uncertainties With Our Picture of Bulge Formation in Major Mergers
The Problem of Giant, Pure-Disk Galaxies: Conclusion

UNIVERSAL SCALING RELATIONS FOR ALL GALAXIES?

COEVOLUTION OF SUPERMASSIVE BLACK HOLES AND HOST GALAXIES
Correlations Between BH Mass and Host Galaxy Properties from Kormendy & Ho (2013)
AGN Feedback and the Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies

QUENCHING OF STAR FORMATION

A PARTIAL SUMMARY OF OUTSTANDING PROBLEMS

REFERENCS

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