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Where Does the Disk Turn Into the Halo? Cool HI in the Outer Milky Way Disk

Published online by Cambridge University Press:  17 September 2012

J.M. Dickey
J.M. Dickey*
Affiliation:
University of Tasmania, Maths and Physics - Bag 37, Hobart, TAS 7005, Australia
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Abstract

Using HI absorption spectra taken from the recent surveys of λ 21-cm line and continuum emission in the Galactic plane, the distribution of cool atomic clouds in the outer disk of the Milky Way is revealed. The warp of the midplane is clearly seen in absorption, as it is in emission, and the cool, neutral medium also shows flaring or increase in scale height with radius similar to that of the warm atomic hydrogen. The mixture of phases, as measured by the fraction of HI in the cool clouds relative to the total atomic hydrogen, stays nearly constant from the solar circle out to about 25 kpc radius. Assuming cool phase temperature ∼50 K this indicates a mixing ratio of 15% to 20% cool HI, with the rest warm.

Type
Research Article
Information
European Astronomical Society Publications Series , Volume 56: The Role of the Disk-Halo Interaction in Galaxy Evolution: Outflow vs. Infall? , 2012 , pp. 205 - 208
Copyright
© EAS, EDP Sciences, 2012

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