The following document lists the file abstract/PVDWERF_DISKS.abs
from catalogue VI/111.
A plain copy of the file
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The pressure of the interstellar medium is a parameter of fundamental importance in steady-state models of a multiphase interstellar medium. However, this quantity is exceedingly difficult to measure. ISO provides a unique opportunity to improve this situation with measurements of the 158 micron CII line. This line is an excellent pressure probe for the atomic medium. We thus propose to use LWS to obtain 1-dimensional strip maps over the ENTIRE HI disks in a small number of nearby face-on and edge-on galaxies in the 158 micron CII line. We will thus derive the pressure in the cold medium as a function of galactocentric radius. More limited strip maps in the NII 122 micron line will be used to derive the contribution of the warm ionized medium to the CII line intensity, the relative proportions of warm ionized medium and neutral medium and their dependence on galactocentric radius. These measurements will form a fundamental test for steady-state models of a multiphase interstellar medium in pressure equilibrium. We will in addition obtain deep CII 158 micron spectra in 2 objects BEYOND the edge of the HI disks, in order to test the hypothesis that in these regions the HI disks become ionized by the extragalactic radiation field, which would have profound implications for our understanding of the outer regions of galaxies, sizes of galactic gaseous disks, statistics of low redshift Lyman alpha systems etc. For our target objects, we have state-of-the-art HI imaging from the VLA and WSRT, mostly unpublished, with excellent sensitivity, which will form the necessary background for interpreting the ISO data. Since thermal pressure in the interstellar medium can essentially only be probed by CII line and HI column density data, the proposed ISO observations are the only way in which these fundamental tests can be made.