Distances of 21cm High Velocity (Oort) Clouds

Details Distances of 21cm High Velocity (Oort) Clouds Distances of 21cm High Velocity (Oort) Clouds

Jul 1984

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984iue..prop.1920y&link_type=abstract

IUE Proposal ID #IGGDY

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Scientific paper

It has been known for about 20 years that high velocity 21 cm clouds (( |v(lsr)|>100 km s^-1) exist at high latitudes in the Galaxy. The origin of these clouds is not known. They may be anywhere from 1 to 100 kpc from the galactic disk. No mass estimates exist, save those using 21 cm fluxes, assumed distances, and assumed fractional ionizations. The properties of these clouds in other species, such as Mg I, Mg II, C II, Si III, C IV or Si IV are largely unknown. The clouds may be typical of systems in other galaxies. If they are generic to most galaxies, they may account for the large velocity widths seen in QSO absorption line systems, whatever their origin. Demonstrating the origin of these clouds (ejecta of supernova explosions, extensions of galactic spiral arms, infalling intergalactic gas, orbiting trash in the local group) depends on determining their distances. We propose a preliminary program aimed at determining properties and distances of these clouds. 1) We propose to determine what ions exist in or around the clouds by observing distant QSO's and Seyfert galaxies that lie in the direction of the clouds. 2) We propose to study the UV spectra of RR lyrae stars that form ideal probes of the distances to these clouds. 3) We propose to observe objects at a range of distances toward these clouds, on the thesis that rough distances are known once absorption lines at the cloud velocity are seen in the spectrum of an object of known distance (and not seen in spectra of closer objects).

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