Observation of neutral hydrogen 21-cm absorption toward double sources

Details Observation of neutral hydrogen 21-cm absorption toward double sources Observation of neutral hydrogen 21-cm absorption toward double sources

May 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985a%26a...146..223c&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 146, no. 2, May 1985, p. 223-234. Research supported by the Observatoire de Pa

Astronomy and Astrophysics

Astrophysics

41

Absorption Spectra, Astronomical Spectroscopy, Centimeter Waves, Hydrogen Clouds, Milky Way Galaxy, Neutral Gases, Data Acquisition, Data Reduction, Kolmogoroff Theory, Molecular Clouds, Normal Density Functions, Optical Thickness, Radio Interferometers, Spectral Energy Distribution

Scientific paper

In order to study the small-scale structure of galactic neutral hydrogen, 21-cm absorption spectra have been measured toward background double sources. Seven sources were observed with the Westerbork Synthesis Radio Telescope, with component separations ranging from a few seconds to a few minutes of arc. Typical absorption variations of about 0.1 in optical depth are detected over scale-lengths less than 1 pc, and 0.2 to 0.3 over lengths greater than 1 pc. No structure is tractable below 0.2 pc, suggesting the existence of a threshold. This is consistent with a minimum diameter of about 1.5 pc for cold H I clouds. A decomposition of the profiles into Gaussian components suggests that the absorption variations are due to velocity variations rather than cloudlet fluctuations. These velocity variations would be due to ordered motions or random turbulent motions.

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