Issue |
A&A
Volume 466, Number 2, May I 2007
|
|
---|---|---|
Page(s) | 555 - 564 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20065796 | |
Published online | 05 February 2007 |
Gaussian decomposition of
surveys
III. Local
1
Tartu Observatory, 61 602 Tõravere, Tartumaa, Estonia e-mail: urmas@aai.ee
2
Argelander-Institut für Astronomie, Universität Bonn (Founded by merging of the Sternwarte, Radioastronomisches Institut and Institut für Astrophysik und Extraterrestrische Forschung der Universität Bonn.) , Auf dem Hügel 71, 53 121 Bonn, Germany e-mail: pkalberla@astro.uni-bonn.de
Received:
10
June
2006
Accepted:
28
January
2007
Aims.We investigate the properties of the 21-cm radio-lines of
galactic neutral hydrogen by decomposing, the profiles of “The
Leiden/Argentine/Bonn (LAB) Survey of Galactic ” into Gaussian components.
The width distribution of the obtained components is analysed
and compared with similar studies by other authors.
Methods.The study is based on an automatic profile decomposition
algorithm. As the Gaussians obtained for the complex
profiles near the galactic plane cannot be directly interpreted
in terms of the properties of gas clouds, we mainly study the
selected simplest profiles in a limited velocity range. The
selection criteria are described and their influence on the
results is discussed.
Results.Considering only the simplest profiles, we
demonstrate that for Gaussians with relatively small LSR
velocities (-9
4 km s-1) it
is possible to distinguish three or four groups of preferred
line-widths. The mean widths of these groups are FWHM =
3.9 ± 0.6, 11.8 ± 0.5, 24.1 ± 0.6, and 42 ±
5 km s-1. Verschuur previously proposed similar
line-width regimes, but with somewhat larger widths. He used a
human-assisted decomposition for a nearly 50 times smaller
database and we discuss systematic differences in analysis and
results.
Conclusions.The line-widths of about 3.9 and 24.1 km s-1 are
well understood in the framework of traditional models of the
two-phase interstellar medium. The components with the widths
around 11.8 km s-1 indicate that a considerable
fraction (up to about 40%) of the gas is thermally
unstable. The reality and the origin of the broad lines with the
widths of about 42 km s-1 is more obscure. These,
however, contain only about 4% of the total observed column
densities.
Key words: ISM: atoms / solar neighbourhood / radio lines: ISM
© ESO, 2007
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