Issue |
A&A
Volume 514, May 2010
|
|
---|---|---|
Article Number | A27 | |
Number of page(s) | 7 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/200913349 | |
Published online | 06 May 2010 |
Gaussian decomposition of
surveys
V. Search for very cold clouds
Tartu Observatory, 61 602 Tõravere, Tartumaa, Estonia e-mail: urmas@aai.ee
Received:
25
September
2009
Accepted:
20
January
2010
Context. In the previous papers of this series, we decomposed all the
21-cm line profiles of the Leiden-Argentina-Bonn
(LAB) database into Gaussian components (GCs), and studied the
statistical distributions of the obtained GCs.
Aims. Now we are interested in separating the “clouds” of similar closely spaced GCs from the general database of the components. In this paper we examine the most complicated case for our new cloud-finding algorithm – the clouds of very narrow GCs.
Methods. To separate the clouds of similar GCs, we started with the
single-link hierarchical clustering procedure in
five-dimensional (longitude, latitude, velocity, GC width, and
height) space, but made some modifications to accommodate it to
the large number of components. We also used the requirement
that each cloud may be represented at any observed sky position
by only one GC and take the similarity of global properties of
the merging clouds into account. We demonstrate that the
proposed algorithm enables us to find the features in gas
distribution, which are described by similar GCs. As a test, we
applied the algorithm for finding the clouds of the narrowest
21-cm line components.
Results. Using the full sky search for cold clouds, we easily detected the
coldest known clouds and demonstrate that actually
they are a part of a long narrow ribbon of cold clouds. We
modeled these clouds as a part of a planar gas ring, then
deduce their spatial placement and discuss their relation to
supernova shells in the solar neighborhood. Many other
narrow-lined
structures are also found. We conclude
that the proposed algorithm satisfactorily solves the posed
task. In testing the algorithm, we found a long ribbon of very
cold
clouds and demonstrated that all the observed
properties of this band of clouds are described very well by
the planar ring model.
Conclusions. We also guess that the study of the narrowest 21-cm
line components may be a useful tool for finding the structure
of neutral gas in solar neighborhood.
Key words: ISM: atoms / ISM: clouds / radio lines: ISM
© ESO, 2010
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