The following document lists the file abstract/MGUELIN_GALEDGE.abs
from catalogue VI/111.
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The outermost parts of galaxies are among the most fascinating, yet the less known regions of the Universe. Although the large optical/ radio nebulae have sizes of 30 kpc or so, circumgalactic matter is observed at distances of 100 kpc from their nuclei. These extreme regions could be the hideouts of dark matter; their slow revolution and low stellar activity has kept them in many respects similar to protogalactic clouds. Obviously, the difficulty of studying the outer parts of galaxies comes from their faintness at all wavelengths. These regions have very low densities and, in their densest parts, are very cold. They are difficult to detect, except in absorption in the lines of sight to bright quasars, or as diffuse sources of X-ray emission. Progresses in their study relies on tracers which could be observed in emission with a high angular resolution. Thermal emission from dust grains may be the best such tracer, and ISO, with its exceptional sensitivity in the FIR, offers an unique opportunity for this study. The detection of bright FIR, submm and mm continuum emission in high redshift galaxies, and the detection of C, O, and CO lines in some of these objects, show that heavy elements and dust were abundant in the `primordial' gas and must be present in the circumgalactic matter. Dust grains, in the vicinity of bright galaxies are likely to have temperatures > 10 K; their thermal emission should peak between 150 and 200 micro-m, beyond the IRAS spectral range, and should be detectable by ISOPHOT. We propose to search for this emission with the PHOT-C200 detector around a sample of nearby galaxies: interacting galaxies with HI bridges and companions, isolated galaxies with and withoout HI warps, edge-on galaxies with conspicious radio or optical halos.