Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984phdt.........4k&link_type=abstract
Ph.D. Thesis California Univ., Berkeley.
Astronomy and Astrophysics
Astronomy
2
Absorption Spectra, Antenna Arrays, Galaxies, Radio Astronomy, Very Long Base Interferometry, Clouds, Cosmic Dust, Electron Spin, Hydrogen, Mathematical Models, Radio Interferometers, Receivers, Very Large Array (Vla)
Scientific paper
Various galactic phenomena were studied using the 21-cm HI line in absorption as a probe. An observing technique developed and used at the Very Large Array and a spectral line interferometer built at Arecibo is described. With these instruments a low-latitude HI-absorption survey was conducted which obtained very sensitive absorption spectra towards 3C123 and 3C147 and the reliability of single dish absorption-spectra towards weak sources at high latitudes was evaluated. Preliminary analysis of the low latitude survey indicates that the mid-plane density of HI in the inner galaxy is 0.5/cu.cm. after accounting for optical depth effects. A model independent proof that the fraction of Not-Strongly Absorbing Hl increases with the absolute value of Z is found. For the first time, the spin temperature of intercloud HI is between 1000 K and 2000 K. Using the existing absorption data, a new model was proposed for the HI vertical structure which accounts for the existence of high-z HI and the thermal electron layer in a self-consistent fashion.
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