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The HI structure of the nuclear disk

Published online by Cambridge University Press:  14 August 2015

R. J. Cohen
R. J. Cohen*
Affiliation:
University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire, SK11 9DL England

Extract

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It is nearly twenty years since Rougoor & Oort (1960) reported the discovery of neutral hydrogen (HI) emission from the galactic nucleus, and I would like to summarize some of the progress that has been made since then in observing and interpreting this emission. One of the most surprising properties to be found is the tilt of the HI distribution relative to the galactic equator. This was noted originally by Kerr (1967), and recent measurements indicate that the tilt is present from within 200 pc of the centre out to a distance of some 2 kpc. (Cohen & Davies 1976, 1978). Because of the tilted distribution the properties of the nuclear emission cannot always be deduced from observations at zero galactic latitude. For example, Rougoor & Oort (1960) deduced a sharp cut-off in the negative-velocity “nuclear disk” emission at ℓ ≃ −4°, from their measurements near zero latitude, whereas the more extensive observations by Kerr (1967) show that the cut-off is only an apparent effect. In reality the emission continues to more negative longitudes, but at higher galactic latitude because of the tilt.

Type
VI. THE GALACTIC NUCLEUS
Information
Symposium - International Astronomical Union , Volume 84: The Large-Scale Characteristics of the Galaxy , 1979 , pp. 337 - 340
Copyright
Copyright © Reidel 1979 

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