Book contents
- Frontmatter
- Contents
- Preface to the Second Edition
- Preface to the First Edition, 2000
- Acknowledgments
- PART I Basic Phenomenology
- PART II Physical Models
- PART III Spiral Galaxies
- 13 Orbits
- 14 The Basic State: Vertical and Horizontal Equilibrium of the Disk
- 15 Density Waves
- 16 Roles of Gas
- 17 Global Spiral Modes
- 18 Spiral Structure in Galaxies
- 19 Bending Waves
- 20 Dark Matter in Spiral Galaxies
- PART IV Elliptical Galaxies
- PART V In Perspective
- Bibliography
- Index of objects
- Index
19 - Bending Waves
from PART III - Spiral Galaxies
Published online by Cambridge University Press: 05 June 2014
- Frontmatter
- Contents
- Preface to the Second Edition
- Preface to the First Edition, 2000
- Acknowledgments
- PART I Basic Phenomenology
- PART II Physical Models
- PART III Spiral Galaxies
- 13 Orbits
- 14 The Basic State: Vertical and Horizontal Equilibrium of the Disk
- 15 Density Waves
- 16 Roles of Gas
- 17 Global Spiral Modes
- 18 Spiral Structure in Galaxies
- 19 Bending Waves
- 20 Dark Matter in Spiral Galaxies
- PART IV Elliptical Galaxies
- PART V In Perspective
- Bibliography
- Index of objects
- Index
Summary
The gas layer of our Galaxy is known to be warped in a rather asymmetric way. Outside the solar circle, the HI disk reaches ≈ 3 kpc above the plane on one side (in the North), whereas it extends down to only 1 kpc below the plane on the other side (in the South); in the outermost regions, at a galactocentric radius of ≈ 30 kpc, the warp is found to reach the height of 6 kpc. Many galaxies are affected by similar global distortions of the disk (Fig. 19.1; see also Fig. 3.4 in Part I). In a survey of twenty-six edge-on galaxies, twenty were found to be warped in HI, often in an asymmetric way, with the warp usually starting at the edge of the optical disk. Warps also have been noted (although often only as marginal evidence) for the stellar disk. The fact that stars and gas both participate in the warp is an indication that the phenomenon is probably dominated by gravitational forces. The presence of significant warps only in the outer regions, where the stellar disk ends, may simply be due to the small inertia of the disk in the outer parts compared with the heavier inner regions.
Besides the frequent integral-sign appearance (i.e., dominance of an m = 1 relatively open distortion of the disk), the morphology of warps is not as well documented.
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- Dynamics of Galaxies , pp. 266 - 279Publisher: Cambridge University PressPrint publication year: 2014