It has been more than five decades ago that Henk van de Hulst predicted the observability of the 21-cm line of neutral hydrogen (HI ). Since then use of the 21-cm line has greatly improved our knowledge in many fields and has been used for galactic structure studies, studies of the interstellar medium (ISM) in the Milky Way and other galaxies, studies of the mass distribution of the Milky Way and other galaxies, studies of spiral struc ture, studies of high velocity gas in the Milky Way and other galaxies, for measuring distances using the Tully-Fisher relation etc. Regarding studies of the ISM, there have been a number of instrumen tal developments over the past decade: large CCD's became available on optical telescopes, radio synthesis offered sensitive imaging capabilities, not only in the classical 21-cm HI line but also in the mm-transitions of CO and other molecules, and X-ray imaging capabilities became available to measure the hot component of the ISM. These developments meant that Milky Way was no longer the exclusive playground for ISM studies and that by reaching out to other galaxies astronomy had gained the advantage of having an "outside" view, though at the expense of giving up some linear resolution. Studies of the ISM in other galaxies are intimately connected to studies of the ISM in the Milky Way.
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ISBN-13
978-94-011-5620-2 (9789401156202)
DOI
10.1007/978-94-011-5620-2
Schweitzer Klassifikation
1 Dust in the Disks of Galaxies.- 1 Introduction.- 2 Dust models and their consequences.- 3 Heating sources and phases of the dust.- 4 The fate of dust in the ISM, and future instruments.- 5 Conclusion.- 2 Molecular Gas in Galaxy Disks.- 1 Introduction.- 2 How well can we measure the mass of molecular gas?.- 3 H2 vs. HI.- 4 Spiral structure in the outer disks.- 5 The central few kiloparsecs.- 6 Circumnuclear regions.- 7 Vertical distribution of molecular gas.- 8 Gas disks around active galactic nuclei.- 3 Cool HI Disks in Galaxies.- 1 Introduction.- 2 Neutral Hydrogen Content and Global Properties.- 3 Distribution of HI in Disks.- 4 HI as a Tracer of the Mass Distribution.- 5 Relationship of ?HI to Star Formation.- 6 Environmental Effects.- 7 Future prospects.- 4 The Warm Ionized Medium and the Disk-Halo Connection in Galaxies.- 1 Introduction.- 2 The WIM of the Milky Way.- 3 New Theoretical Developments on the Origin and Maintenance of WIMs.- 4 Observations of Diffuse Ionized Gas in External Galaxies.- 5 Conclusions.- 5 Hot Gas and X-Rays.- 1 Is there Hot Gas in Normal Galaxies?.- 2 Hot Gas in Late Type Galaxies.- 3 Hot Gas in Early Type Galaxies.- 6 Abundance Gradients in Spiral Galaxies.- 1 Introduction.- 2 Background Information.- 3 Results.- 4 Conclusions.- 7 From Gas to Stars: Regulation of Star Formation.- 1 Introduction.- 2 The Schmidt law.- 3 Star formation thresholds.- 4 Regulation of the SFR.- 8 Subject Index.- 9 Object Index.- 10 List of Symbols.
