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

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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