Published in "Gas Accretion onto Galaxies", Astrophysics and Space Science Library, Volume 430. ISBN 978-3-319-52511-2. Springer International Publishing AG, 2017, p. 271.
https://arxiv.org/abs/1612.00448

For a PDF version of the article, click here.

OBSERVATIONAL DIAGNOSTICS OF GAS FLOWS: INSIGHTS FROM COSMOLOGICAL SIMULATIONS

Claude-André Faucher-Giguère


Department of Physics and Astronomy and Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA


Abstract: Galactic accretion interacts in complex ways with gaseous halos, including galactic winds. As a result, observational diagnostics typically probe a range of intertwined physical phenomena. Because of this complexity, cosmological hydrodynamic simulations have played a key role in developing observational diagnostics of galactic accretion. In this chapter, we review the status of different observational diagnostics of circumgalactic gas flows, in both absorption (galaxy pair and down-the-barrel observations in neutral hydrogen and metals; kinematic and azimuthal angle diagnostics; the cosmological column density distribution; and metallicity) and emission (Lyα; UV metal lines; and diffuse X-rays). We conclude that there is no simple and robust way to identify galactic accretion in individual measurements. Rather, progress in testing galactic accretion models is likely to come from systematic, statistical comparisons of simulation predictions with observations. We discuss specific areas where progress is likely to be particularly fruitful over the next few years.


Table of Contents

INTRODUCTION

ABSORPTION DIAGNOSTICS
H I Covering Fractions
Metal Absorption Systems Transverse to Galaxies
Down-the-Barrel Metal Absorption Lines
Kinematic and Azimuthal Angle Diagnostics
Azimuthal Angle Diagnostics
Kinematic Diagnostics
Cosmological Absorber Statistics
The HI Column Density Distribution
The Metallicity Distribution of LLSs

EMISSION DIAGNOSTICS
Lyα Emission from the CGM
UV Metal Line Emission from the CGM
X-ray Emission from Hot Halo Gas

CONCLUSIONS AND OUTLOOK

REFERENCES

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