Published in "Outskirts of Galaxies", Astrophysics and Space Science Library, Volume 434. ISBN 978-3-319-56569-9. Springer International Publishing AG, 2017, p. 209.
https://arxiv.org/abs/1612.05272v1

For a PDF version of the article, click here.

HI IN THE OUTSKIRTS OF NEARBY GALAXIES

A. Bosma


Aix Marseille Univ, CNRS, LAM, Laboratoire d'Astrophysique de Marseille, Marseille, France


Abstract: The Hi in disk galaxies frequently extends beyond the optical image, and can trace the dark matter there. I briefly highlight the history of high spatial resolution Hi imaging, the contribution it made to the dark matter problem, and the current tension between several dynamical methods to break the disk-halo degeneracy. I then turn to the flaring problem, which could in principle probe the shape of the dark halo. Instead, however, a lot of attention is now devoted to understanding the role of gas accretion via galactic fountains. The current Λ cold dark matter theory has problems on galactic scales, such as the core-cusp problem, which can be addressed with Hi observations of dwarf galaxies. For a similar range in rotation velocities, galaxies of type Sd have thin disks, while those of type Im are much thicker. After a few comments on modified Newtonian dynamics and on irregular galaxies, I close with statistics on the Hi extent of galaxies.


Table of Contents

INTRODUCTION

HI IN GALAXIES AND THE DARK MATTER PROBLEM: EARLY WORK

WARPS

FURTHER DATA ON HI IN GALAXIES AND THE DARK MATTER PROBLEM

THE DISK-HALO DEGENERACY IN THE DARK MATTER PROBLEM

FLARING OF THE OUTER HI LAYER: PROBING THE SHAPE OF THE DARK MATTER HALO
Early Work on Case Studies
Recent Results for Small, Flat Galaxies
Large Galaxies with a High Star Formation Rate: Accretion
Velocity Dispersions in the Outer HI Layers of Spiral Galaxies
Star Formation in Warped HI Layers

THE CORE-CUSP PROBLEM

ALTERNATIVE GRAVITY THEORIES

IRREGULAR GALAXIES
Very Large HI Envelopes
Velocity Dispersions in Dwarf Irregular Galaxies

THE RELATION BETWEEN HI EXTENT AND THE OPTICAL RADIUS

CONCLUDING REMARKS

REFERENCES

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