Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997pgh..conf...27w&link_type=abstract
The Physics of Galactic Halos, Proceedings of the 156th WE-Heraeus Seminar, Bad Honnef, Germany, February 11-14, 1996, Eds.: Les
Astronomy and Astrophysics
Astronomy
1
Radio Astronomy, Radio Emission, Radio Observation, Radio Spectra, Radio Telescopes, Galactic Halos, Galactic Structure, Hydrogen Atoms, Neutral Gases, Dispersion, Radial Velocity, Velocity Distribution, Spectral Emission, Emission Spectra, H Lines, Line Spectra, Spectral Line Width
Scientific paper
The existence of an extended gaseous halo of our Galaxy was already proposed by Spitzer (1956). He argued that the clouds which had been seen in absorption far above the galactic plane could only persist there, if a surrounding low-density gas shields them from rapid disintegration. This low-density gas would have to be very hot to mount the necessary pressure ($T\sim 106$~K). Until now, there have been considerable problems both with maintaining such a hot halo (e.g., Schmutzler \& Tscharnuter, 1993) and with the origin/condensation of the cold absorbing clouds in it. Composition, density, temperature and extent of the galactic halo have all been subject to extensive debate. \\ As described by Kalberla et al. (1996a), the new Leiden/Dwingeloo 21-cm line Survey (hereafter LDS) has improved sensitivity of low-level emission by almost a factor of 10 compared with previous Hi surveys. This stimulated us to search for the signature of neutral hydrogen in the galactic halo, i.e. for faint and very broad components in the Hi emission profiles.\\ The basis for the present investigation is the LDS described by Hartmann (1994) and Hartmann \& Burton (1996). We improved the stray radiation correction as described by Hartmann et al. (1996) by taking the ground reflection into account. Various methods have been used to isolate very low-level Hi emission with large velocity dispersions from systematic profile errors and contamination features.
Burton William Butler
Hartmann Dap
Kalberla Peter M. W.
Mebold Ulrich
Westphalen Gernot
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