Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dave.
https://arxiv.org/abs/1612.00513

For a PDF version of the article, click here.

GAS ACCRETION AND ANGULAR MOMENTUM

Kyle R. Stewart


Department of Mathematical Sciences, California Baptist University, 8432 Magnolia Ave., Riverside, CA 92504, USA


Abstract: In this chapter, we review the role of gas accretion to the acquisition of angular momentum, both in galaxies and in their gaseous halos. We begin by discussing angular momentum in dark matter halos, with a brief review of tidal torque theory and the importance of mergers, followed by a discussion of the canonical picture of galaxy formation within this framework, where halo gas is presumed to shock–heat to the virial temperature of the halo, following the same spin distribution as the dark matter halo before cooling to the center of the halo to form a galaxy there. In the context of recent observational evidence demonstrating the presence of high angular momentum gas in galaxy halos, we review recent cosmological hydrodynamic simulations that have begun to emphasize the role of “cold flow” accretion — anisotropic gas accretion along cosmic filaments that does not shock–heat before sinking to the central galaxy. We discuss the implications of these simulations, reviewing a number of recent developments in the literature, and suggest a revision to the canonical model as it relates to the expected angular momentum content of gaseous halos around galaxies.


Table of Contents

INTRODUCTION

ANGULAR MOMENTUM OF DARK MATTER HALOS
Tidal Torque Theory
Angular Momentum Acquisition via Mergers

THE ANGULAR MOMENTUM OF GALAXIES
Modeling Gas Accretion onto Galaxies
Hydrodynamic Simulations of Galaxy Formation

ANGULAR MOMENTUM OF GASEOUS HALOS
Observations of High Angular Momentum Gas
"Cold Flow" Gas Accretion and Angular Momentum
Theoretical Predictions: High Angular Momentum, Co-rotation, and Inspiraling Cold Streams

SUMMARY AND CONCLUSION

REFERENCES

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