Structure of HII regions and their distribution in the galaxy

Thesis/Dissertation · Mon Jan 01 04:00:00 EST 1979

OSTI ID:5604745

Lockman, F J

This dissertation concerns the use of radio recombination lines to determine the structure of HII regions and the distribution of HII regions in the galaxy. The first three chapters treat the formation and transfer of radio recombination lines and examine various processes that effect the ability to deduce nebular properties from radio observations. It is shown that recombination line intensities are influenced, in a non-linear fashion, by the geometric structure of a nebula. If there are variations in the path length through even an isothermal, homogeneous HII region, the line-to-continuum ratio will vary from point to point across the nebula. When observed with an antenna beam, the measured line-to-continuum ratios may be quite different from the true values. Certain analytic shortcuts that are often used in place of a full analysis are discussed and shown to give systematically erroneous results. The behavior of a simple class of inhomogeneous models is examined in detail to show how some information on the nebular temperature, density, and geometry can be determined given adequate data. Comparison of model results with observations of Orion A shows that the nebula must have a specific radial temperature gradient. Nebular expansion is considered, and calculations suggest that this process can broaden lines sufficiently to remove discrepancies between observed and purely thermal linewidths. The distribution of dense HII regions is derived using kinematic models based on circular rotation and density-wave theory.

• Research Organization: Massachusetts Univ., Amherst (USA)
• OSTI ID: 5604745
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC RADIO SOURCES
DENSITY
DISTRIBUTION
ELECTROMAGNETIC RADIATION
EXPANSION
GALAXIES
H2 REGIONS
LINE BROADENING
MATHEMATICAL MODELS
MILKY WAY
MORPHOLOGY
MOTION
PARTICLE KINEMATICS
PHYSICAL PROPERTIES
RADIATIONS
RADIOWAVE RADIATION
ROTATION
SPATIAL DISTRIBUTION
TEMPERATURE MEASUREMENT