AbstractsAstronomy & Space Science

Non-thermal galactic background radiation

by Hilary Vivien,1949- Cane

Institution: University of Tasmania
Year: 1977
Keywords: Radiation
Record ID: 1032451
Full text PDF: http://eprints.utas.edu.au/18772/1/whole_CaneHilaryVivien1978_thesis.pdf


This thesis presents the results and analysis of data obtained using the Llanherne low-frequency array. Surveys of the Galaxy at five frequencies in the range 2 to 20 MHz have been made and the data have been assembled into maps covering the area 320° ≤ ₰ ≤ 30° 30 ° and -25° ≤ b ≤ 22 ° . The data from these maps are combined with data from seven earlier continuum surveys to produce galactic radio spectra in various directions. A summary is made of most of the measurements, at frequencies less than approximately 400 MHz, 'of the galactic background radiation and their interpretation. Two new composite maps, at 10 and 30 MHz, are presented. These, combined with the 85 MHz all-sky map, are used to illustrate the variation of the galactic non-thermal radiation across the sky, and with frequency. The galactic spectra are interpreted in terms of a model of the Galaxy in which synchrotron emission, and absorption in HII regions predominate in spiral arms. However, it is proposed that the synchrotron emission arms and the arms defined by HII regions are not coincident. In addition to the HII absorbing gas the model incorporates a much broader uniform absorbing HI gas which is responsible for high latitude absorption, pulsar signal dispersion and Faraday rotation. For the HI gas it is found that ∫ne2Te¯1.35 dl ≈ 1.1 x 10¯7 cm¯6 K¯1 . 35 pc For the HII gas the above quantity varies for different arms. An average value is ∫ne2Te¯1.35 dl ≈ 2.7 x 10¯6 k¯1.35 pc