EAS Publications Series
Volume 56, 2012The Role of the Disk-Halo Interaction in Galaxy Evolution: Outflow vs. Infall?
|Page(s)||205 - 208|
|Section||Evidence for a Disk-Halo Connection in Galaxies|
|Published online||17 September 2012|
Miguel A. de Avillez (ed)
EAS Publications Series, 56 (2012) 205–208
Where Does the Disk Turn Into the Halo? Cool HI in the Outer Milky Way Disk
University of Tasmania, Maths and Physics - Bag 37, Hobart, TAS 7005, Australia
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.
© EAS, EDP Sciences, 2012